Exploring the Science of Light
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A - prefix meaning "not," from L. a-, short for ab "away from" (cf. avert), or its cognate, Gk. a-, short for apo "away from, from," both cognate with Skt. apa "away from," Goth. af, O.E. of.

Aberration - 1594, "a wandering, straying," from L. aberrationem, from aberrare "go astray," from ab- "away" + errare "to wander." Meaning "deviation from the normal type" first attested 1846.

Absorb - 1490, from M.Fr. absorber (O.Fr. assorbir), from L. absorbere "to swallow up," from ab- "from" + sorbere "suck in." Absorbent (n.) first recorded 1718. Absorbing in the fig. sense of "very interesting" first recorded 1876.

Achromatic - From Gk. akhromatos : a-, "without" + khroma, khromat-, "color."

Afocal - From L. a- "without" and L. focus " hearth, fireplace."

Amorphous - "shapeless," 1731, from Gk. amorphos "without form, shapeless, deformed," from a- "without" + morphe "form."

Amplify - 1432, "to enlarge or expand," from M.Fr. amplifier, from L. amplificare "to enlarge," from amplificus "splendid," from amplus "large" + the root of facere "make, do." Meaning "augment in volume or amount" is from 1580.

Amplitude - 1549, from L. amplitudinem (nom. amplitudo, gen. amplitudinis) "wide extent, width," from amplus.

Angle (n.) - "intersecting lines," c.1384, from L. angulum (nom. angulus) "corner," a dim. form from PIE base *ang-/*ank- "to bend" (cf. Gk. ankylos "bent, crooked," L. ang(u)ere "to compress in a bend, fold, strangle," O.C.S. aglu "corner," Lith. anka "loop," Skt. ankah "hook, bent," O.E. ancleo "ankle," O.H.G. ango "hook").

Aperture - 1649, from L. apertura, from apertus, pp. of aperire "to open," from PIE bases *ap(o)- "away" + *wer- "to close, cover."

Apex - 1601, from L. apex "summit, peak, tip" probably related to apere "to fasten, fix," hence "the tip of anything" (one of the meanings in L. was "small rod at the top of the flamen's cap").

Aplanatic – from Gk. a- "without" and Gk. plansthai "to wander."

Apodize – from Gk. a- "without" and Gk. pod- "feet."

Astigmatism - coined (in form astigmatic) 1849 by English scientist William Whewell (1794-1866), from Gk. a- "without" + stigmatos gen. of stigma "a mark, spot, puncture."

Attenuate (v.) - 1530, from L. attenuatus, pp. of attenuare "to make thin," from ad- "to" + tenuare "make thin," from tenuis "thin."

Axis - 1549, "imaginary straight line around which a body (such as the Earth) rotates," from L. axis "axle, pivot, axis of the earth or sky," from PIE *aks- "axis" (c.f. O.E. eax "axle," Gk. axon, Skt. aksah, Lith. aszis).


Baffle - 1548, "to disgrace," perhaps a Scottish respelling of bauchle "to disgrace publicly" (especially a perjured knight), prob. related to Fr. bafouer "to abuse, hoodwink," possibly from baf, a natural sound of disgust, like bah. Meaning "to bewilder, confuse" is from 1649; that of "to defeat someone's efforts" is from 1675. The noun sense of "shielding device" is first recorded 1881.

Beam - O.E. beam originally "living tree," but by 1000 also "post, ship's timber," from W.Gmc. *baumoz (cf. O.Fris. bam, Du. boom, Ger. Baum "tree"), perhaps from PIE verb root *bu- "to grow." Meaning of "ray of light" developed in O.E., probably because it was used by Bede to render L. columna lucis, Biblical "pillar of fire." The verb meaning "emit rays of light" is from c.1440.

Bifocal - 1888, from bi- + focal (see focus). Conceived by Benjamin Franklin, but called by him double spectacles.

Binocular - 1738, "involving both eyes," from Fr. binoculaire, from L. bini "double" + ocularis "of the eye," from oculus "eye." The double-tubed telescopic instrument (1871, short for binocular glass) earlier was called a binocle (1696).

Blur - 1548, akin to blear. The verb is 1581, from the noun. (blear - c.1300, blere "watery, rheumy.")

Bore - O.E. borian "to bore," from bor "auger," from P.Gmc. *boron, from PIE base *bhor-/*bhr- "to cut with a sharp point" (cf. Gk. pharao "I plow," L. forare "to bore, pierce," O.C.E. barjo "to strike, fight," Alb. brime "hole"). The meaning "diameter of a tube" is first recorded 1572.

Bright - O.E. bryht, by metathesis from beorht "bright, splendid," from P.Gmc. *berkhiaz, from PIE base *bhereg- "to gleam, white" (cf. Goth. bairhts "bright," Skt. bhrajate "shines, glitters," Lith. breksta "to dawn," Welsh berth "bright, beautiful," L. flagrare "to blaze").


Camcorder - 1982, from camera and recorder.

Candle - O.E. candel, early church-word borrowing from L. candela "a light, torch," from candere "to shine," from PIE base *kand- "to glow, to shine."

Cavity - 1541, from M.Fr. cavité, from L.L. cavitas "hollowness," from L. cavus "hollow."

Camera - 16c., in Mod.L. camera obscura "dark chamber" (a black box with a lens that could project images of external objects), from L. camera "vaulted room," from Gk. kamara "vaulted chamber," from PIE base *kam- "to arch." Contrasted with camera lucida (L., "light chamber"), which uses prisms to produce an image on paper beneath the instrument, which can be traced. Shortened to camera when modern photography began, 1840.

Cataract - 1430, from L. cataracta "waterfall," from Gk. katarhaktes "swooping, rushing down," from kata "down" + arhattein "to strike hard." Its alternate sense in L. of "portcullis" was probably passed through M.Fr. to form the Eng. meaning "eye disease" (1547), on the notion of "obstruction."

Catoptric – From G.k katoptrikos, from katoptron, "mirror." Of or relating to mirrors and reflected images.

Chromatic - 1597 (of music), 1831 (of color), from Gk. chromatikos "suited for color," from chroma (gen. chromatos) "color, complexion, character," but also used of music, orig. "skin, surface."

Clad - 1300, alternate pt. and pp. of clothe, from O.E. geclæþd, pp. of clæþan "to clothe," from clað "cloth." The covering of the core in an optical fiber, 1956.

Coherent - c.1555, from M.Fr. cohérent, from L. cohærentem (nom. cohærens), prp. of cohærere "cohere," from com- "together" + hærere "to stick."

Color - c.1225, from O.Fr. colur, from L. color (acc. colorem) "color, hue," from O. L. colos, orig. "a covering" (akin to celare "to hide, conceal"), from PIE base *kel- "hide." O.E. words for "color" were hiw, bleo. The verb is from c.1300, earliest use is figurative.

Collimate – From L.L. collimare, collimat-, alteration of L. collineare "to aim" and/or com- + L. lineare," to make straight."

Collision - c.1432, from M.Fr. collision, from L. collisionem (nom. collisio), from collidere (see collide).

Concave - 14c., from L. concavus "hollow," from com- intensive prefix + cavus "hollow."

Concentric - 1391, from O.Fr. concentrique, from M.L. concentricus, from com- "together" + centrum "circle, center."

Condenser – From M.E. condensen, from O.F. condenser, from L. condensare "reduce volume or compass of."

Cone - 1562, from L. conus "a wedge, peak, cone," from Gk. konos "cone, spinning top, pine cone," from PIE base *ko(n)- "to sharpen."

Confocal – From L. conducere "to lead together" and L. focus " hearth, fireplace."

Conjugation - c.1450, from L. conjugationem, from conjugare "to join together."

Convex - 1571, from M.Fr. convexe, from L. convexus "vaulted, arched," pp. of convehere "to bring together," from com- "together" + vehere "to bring." Possibly from the idea of vaults carried together to meet at the point of a roof.

Core - 1398, probably from O.Fr. coeur "core of fruit, heart of lettuce," lit. "heart," from L. cor "heart." Center of an optical fiber, 1956.

Curve - early 15c., from L. curvus "crooked, curved, bent."


Decay - c.1460, from O.Fr. decair, from V.L. *decadere "to fall off," from L. cadere "to fall," from PIE *kad- "to fall." Meaning "gradual decrease in radioactivity" is from 1897.

Detect - 1447, from L. detectus, pp. of detegere "uncover, disclose," from de- "un-, off" + tegere "to cover."

Diffraction - 1671, from Fr. diffraction, from Mod.L. diffractionem, from L. diffrac-, stem of diffringere "break in pieces," from dis- "apart" + frangere "to break."

Diffusion - c.1374, from L. diffusionem, from stem of diffundere "scatter, pour out," from dif- "apart, in every direction" + fundere "pour."

Diopter - From L. dioptra, from Gk. dioptra : dia- + optos, "visible." A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.

Disperse - c.1450, from M.Fr. disperser "scatter," from L. dispersus, pp. of dispergere "to scatter," from dis- "apart, in every direction" + spargere "to scatter."

Distort - 1586, from L. distortus, pp. of distorquere "to twist different ways, distort," from dis- "completely" + torquere "to twist."

Doppler - 1871, in reference to Christian Doppler (1803-53), Austrian scientist, who in 1842 explained the effect of relative motion on waves (originally to explain color changes in binary stars); proved by musicians performing on a moving train. Doppler shift is the change of frequency resulting from the Doppler effect.

Double - c.1225, from O.Fr. duble, from L. duplus "twofold," from duo "two" + -plus "fold."


Ellipse - 1656 (implied in ellpitical), from Fr. ellipse, from L. ellipsis "ellipse," also, "a falling short, deficit," from Gk. elleipsis (see ellipse), because the conic section of the cutting plane makes a smaller angle with the base than does the side of the cone, hence, a "falling short." First applied by Apollonius of Perga (3c. B.C.E.).

Ellipsis - 1570, from L. ellipsis, from Gk. elleipsis "a falling short, defect, ellipse," from elleipein "to fall short, leave out," from en- "in" + leipein "to leave."

Emission - 1607, from L. emissionem (nom. emissio) "a sending out," from emiss-, stem of emittere "send out" (see emit).

Emit - 1623, from L. emittere "send forth," from ex- "out" + mittere "to send."

Energy - 1599, from M.Fr. energie, from L.L. energia, from Gk. energeia "activity, operation," from energos "active, working," from en- "at" + ergon "work." Used by Aristotle with a sense of "force of expression;" broader meaning of "power" is first recorded in Eng. 1665.

Etalon - Early 20c, Fr. étalon, from earlier estalon, "standard of weights and measures."

Etendue - Fr. for "extent" or "space."

Eye - O.E. ege (Mercian), eage (W. Saxon), from P.Gmc. *augon, from PIE *oqw- "to see" (cf. Goth. augo, O.C.S. oko, L. oculus, Armenian aku). Until c.1375 the plural was in -an, hence modern dial. plural een, ene.


Fiber - 1540, from Fr. fibre, from O.Fr. fibre, from L. fibra "a fiber, filament," of uncertain origin, perhaps related to L. filum "thread," or from root of findere "to split." Fiber optics is from1956.

Field (n.) - O.E. feld "plain, open land" (as opposed to woodland), also "a parcel of land marked off and used for pasture or tillage," probably related to O.E. folde "earth, land," from P.Gmc. *felthuz "flat land," from PIE *pel(e)-tu-, from base *pele- "flat, to spread" (cf. L. planus "flat, level," O.C.S. polje "field"). Common W.Gmc. (cf. O.Fris. feld, M.H.G. velt, Ger. Feld), but not found outside it (Sw. fält, Dan. felt are borrowed from Ger.), though Finnish pelto "field" is believed to have been adapted from P.Gmc.

Film - O.E. filmen "membrane, skin," from W.Gmc. *filminjan (cf. O.Fris. filmene "skin," O.E. fell "hide"), extended from P.Gmc. *fello(m) "animal hide," from PIE *pello-/*pelno- (cf. Gk. pella, L. pellis "skin"). Sense of "a thin coat of something" is 1577, extended by 1845 to the coating of chemical gel on photographic plates. By 1895 this also meant the coating plus the paper or celluloid.

Filter (n.) - c.1400, from M.L. filtrum "felt," which was used to strain impurities from liquid, from W.Gmc. *filtiz.

Focus - 1644, from L. focus "hearth, fireplace," of unknown origin, used in post-classical times for "fire" itself, taken by Kepler (1604) in a mathematical sense for "point of convergence," perhaps on analogy of the burning point of a lens (the purely optical sense of the word may have existed before 1604, but it is not recorded).

Frequent - 1531, from L. frequentem (nom. frequens) "crowded, repeated," of uncertain origin. The v. (1477) is from L. frequentare "visit regularly." Frequency (1551) came to be used 1831 in physics for "rate of recurrence," especially of a vibration.

Fringe - 1354, from O.Fr. frenge (1316), from V.L. *frimbia, metathesis of L. fimbriæ (pl.) "fibers, threads, fringe," of uncertain origin. Figurative sense of "outer edge, margin," is first recorded 1894.


Glass - O.E. glæs, from W.Gmc. *glasam (cf. M.Du. glas, Ger. Glas), from P.Gmc. base *gla-/*gle-, from PIE *gel-/*ghel- "to shine, glitter, be green or yellow," a color word that is the root of words for grey, blue, green, and yellow (cf. O.E. glær "amber," L. glaesum "amber," O.Ir. glass "green, blue, gray," Welsh glas "blue").

Grate (n.) - c.1400, from M.L. grata "lattice," from L. cratis "wickerwork."

Grind - O.E. grindan, forgrindan "destroy by crushing" (class III strong verb; past tense grand, pp. grunden), from P.Gmc. *grindanan (cf. Du. grenden), related to ground, from PIE *ghrendh- "crushing" (cf. L. frendere "to gnash the teeth," Gk. khondros "corn, grain," Lith. grendu "to scrape, scratch").

Gyroscope - 1856, invented and named in Fr. 1852 by Foucault, from Gk. gyros "circle" + skopos "watcher," because the device demonstrates that the earth rotates.


Harmonic - 1531 (implied in harmonical), from L. harmonicus, from Gk. harmonikos "harmonic, musical," from harmonia.

Hologram - 1949, coined by Hungarian-born British scientist Dennis Gabor, 1971 Nobel prize winner in physics for his work in holography, from Gk. holos "whole" (in sense of three-dimensional) + -gram. Holography "process of using holograms" coined 1964 from hologram on analogy of telegraphy/telegram.

Homogeneous - 1641, from M.L. homogeneus, from Gk. homogenes "of the same kind," from homos "same" + genos "kind, gender, race, stock."


Illumination - from L. illuminationem (nom. illuminatio), from illuminare "to throw into light," from in- "in" (with assimilation of -n- to the following consonant) + lumen (gen. luminis) "light." Meaning "the action of lighting" is from 1563. Illuminate (M.E. enlumyen) originally meant "decorate written material with gold, silver, bright colors;" sense of "shining light on" first recorded 1563. (Illumine in this sense is from 1375.)

Illusion - c.1340, "act of deception," from O.Fr. Sense of "deceptive appearance" developed in Eng. c.1374. Illusionist "conjurer, magic act performer" is from 1850.

Image - c.1225, "artificial representation that looks like a person or thing," from O.Fr. image, earlier imagene (11c.), from L. imaginem (nom. imago) "copy, statue, picture, idea, appearance," from stem of imitari "to copy, imitate" (see imitate). Meaning "reflection in a mirror" is c.1315. The mental sense was in L., and appears in Eng. c.1374.

Impulse - 1432 (implied in impulsion) "an act of impelling, a thrust, push," from L. impulsus "a push against, pressure, shock," also "incitement, instigation," pp. of impellere.

Interface - 1962 (n.), 1967 (v.), from inter- + face.

Interfere - 1440, "to strike against," from M.Fr. enterferer "to strike each other," from entre- "between" + ferir "to strike," from L. ferire "to knock, strike," related to L. forare "to bore, pierce," and cognate with O.E. borian "to bore" (cf. punch (v.), which has both the sense "to hit" and "to make a hole in").

Iris – From M.E., iris (the plant); from L. iris, irid-, "rainbow, iris (the plant)"; from Gk., rainbow, brightly-colored gemstone, iris of the eye. It regulates the amount of light entering the eye.

Irradiate - 1603, "to cast beams of light upon," from L. irradiatus, pp. of irradiare "shine forth," from in- "in" + radiare "to shine" (see radiate).


Laser - 1960, acronym for "light amplification by stimulated emission of radiation."

Lens - 1693, from L. lens (gen. lentis) "lentil," on analogy of the double-convex shape.

Light (n.) - "brightness," O.E. leht, earlier leoht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- "light, brightness" (cf. Skt. rocate "shines;" Arm. lois "light," lusin "moon;" Gk. leukos "bright, shining, white;" L. lucere "to shine," lux "light," lucidus "clear;" O.C.S. luci "light;" Lith. laukas "pale;" Welsh llug "gleam, glimmer;" O.Ir. loche "lightning," luchair "brightness;" Hittite lukezi "is bright"). The -gh- was an Anglo-Fr. scribal attempt to render the O.E. hard -h- sound, which has since disappeared.

Loss - O.E. los "loss, destruction," from P.Gmc. *losom- (cf. O.N. los "the breaking up of an army"), from PIE *lau-. The modern word, however, probably evolved 14c. from lost, the original pp. of lose.

Lucent - "shining, bright, luminous," c.1500, from L. lucentem, prp. of lucere "to shine" (see light (n.)).

Lumen – L. lumen, "an opening, light." A unit of light in the SI system.

Luminary - c.1450, "source of (artificial) light," from M.Fr. luminarie "lamp, light," from L.L. luminare "light, torch, lamp, heavenly body," lit. "that which gives light," from L. lumen (gen. luminis) "light." Luminosity in astronomy sense of "intrinsic brightness of a heavenly body" (as distinguished from apparent magnitude, which diminishes with distance), is attested from 1906.

Luminous - 1432, "full of light," from L. luminosus "shining, full of light," from lumen (gen. luminis) "light," related to lucere "to shine."

Lunar – M.E., "crescent-shaped," from O.Fr. lunaire, from Latin lunaris, "of the moon," from luna, "moon."


Magnify - c.1380, "to speak or act for the glory or honor (of someone or something)," from O.Fr. magnifier, from L. magnificare "esteem greatly, extol," from magnificus "splendid" (see magnificence). Meaning of "use a telescope or microscope" is first attested 1665.

Maser - m(icrowave) a(mplification by) s(timulated) e(mission of) r(adiation).

Meniscus - "crescent-shaped body," 1693 in ref. to lenses, c.1812 in ref. to liquid surfaces, Mod.L. meniscus, from Gk. meniskos "lunar crescent," dim. of mene "moon."

Meter – From Fr. -mètre, and Gk. metron, "measure." Measuring device. "unit of length," 1797, from Fr. mètre, from Gk. metron "measure," from PIE base *me- "measure" (cf. Gk. metra "lot, portion," Skt. mati "measures," matra "measure," Avestan, O.Pers. ma-, L. metri "to measure"). Developed by Fr. Academy of Sciences for system of weights and measures based on a decimal system originated 1670 by Fr. clergyman Gabriel Mouton. Originally intended to be one ten-millionth of the length of a quadrant of the meridian.

Microscope - 1656, from Mod.L. microscopium, lit. "an instrument for viewing what is small," from Gk. micro- (q.v.) + -skopion. "means of viewing," from skopein "look at."

Mirror - c.1225, from O.Fr. mireor "a reflecting glass," earlier miradoir (11c.), from mirer "look at," from V.L. *mirare, from L. mirari "to wonder at, admire." Fig. usage is attested from c.1300. The verb. meaning "to reflect" is first attested 1820 in Keats's "Lamia."

Modulation - 1398, "act of singing or making music," from O.Fr. modulation "act of making music," from L. modulationem (nom. modulatio) "rhythmical measure, singing and playing, melody," from modulatus, pp. of modulari "regulate, measure off properly," from modulus (see module). Meaning "act of regulating according to measure or proportion" is from 1531.

Moiré (n.) - Fr. pp. of moirer, "to water," from mouaire, moire. Probably alteration of Eng. mohair. Having a wavy or rippled surface pattern. Moire effect: superimposing a repetitive design, such as a grid, on the same or a different design in order to produce a pattern distinct from its components.

Mono - from Gk. mono-, comb. form of monos "single, alone," from PIE base *men- "small, isolated," also represented by Gk. manos "rare, sparse," and perhaps by Eng. minnow.

Monocle - 1886, "single eyeglass," from Fr. monocle, from L.L. monoculus "one-eyed," from Gk. monos "single, alone" + L. oculus "eye."


Nodal – Originally M.E., lump in the flesh, from L. nodus, knot."


Objective - 1620, originally in the philosophical sense of "considered in relation to its object" (opposite of subjective), formed on pattern of M.L. objectivus, from objectum "object." The lens or lens system in a microscope or other optical instrument that first receives light rays from the object and forms the image.

Obstruction – From L. obstruere, obstruct- : ob-, "against." One that obstructs; an obstacle.

Optic - 1541, from M.Fr. optique, obtique (c.1300), from M.L. opticus "of sight or seeing," from Gk. optikos "of or having to do with sight," from optos "seen, visible," from op-, root of opsesthai "be going to see," related to ops "eye," from PIE *oqw- "eye/see" (see eye). Optics "science of sight and light" is from 1579; optician is first attested 1687, after Fr. opticien.

Oscillation - 1658, from Fr. oscillation, from L. oscillationem (nom. oscillatio), pp. of oscillare "to swing," supposed to be from oscillum "little face," lit. "little mouth," a mask of open-mouthed Bacchus hung up in vineyards to swing in the breeze.


Parabola - 1579, from Gk. parabole "parabola, application," so called by Apollonius of Perga c.210 B.C.E. because it is produced by "application" of a given area to a given straight line.

Periodic - 1642, from Fr. périodique (14c.), from L. periodicus, from periodus.

Periscope - 1899, formed in Eng. from peri- "around" + -scope "instrument for viewing." Earlier (1865) a technical term in photography.

Perturb - c.1374 (implied in perturbation), probably via O.Fr. perturber (14c.), from L. perturbare "to confuse, disorder, disturb," from per- "through" + turbare "disturb, confuse," from turba "turmoil, crowd."

Phase - 1812, "phase of the moon," back-formed from Mod.L. phases, pl. of phasis, from Gk. phasis "appearance" (of a star), "phase" (of the moon), from stem of phainein "to show, to make appear." L. sing. phasis was used in Eng. from 1660. Non-lunar application is first attested 1841.

Photocopy (v.) - 1924 in the sense of "make a photographic reproduction," from photo- "light" + copy (q.v.). The usual modern meaning arose 1942 with the advent of xerography. The noun is recorded from 1934. Photostat (1911) was a type of copying machine (trademark Commercial Camera Company, Providence, R.I.) whose name became a generic noun and verb (1914) for "photocopy."

Photograph (n.) - 1839, "picture obtained by photography," coined by Sir John Herschel from photo- + -graph "instrument for recording." The verb and photography also are first attested 1839, all from a paper read before the Royal Society on March 14, 1839.

Photography – 1839, from Gk. phos, phot- 'light' and graphos 'writing'. Lit., photography means 'light recording'.

Photon - "unit of electromagnetic radiation," 1926, from photo- "light" + on "unit."

Plane - "flat surface," 1604, from L. plantum "flat surface," properly neut. of adj. planus "flat, level," from PIE *plat- "spread out, broad, flat" (cf. Skt. prathati "spreads out;" Gk. platys "broad;" Hitt. palhi "broad;" Lith. platus "broad," plonas "thin;" Ger. Fladen "flat cake;" O.Ir. lethan "broad").

Polarize - 1811, from Fr. polariser, coined by Fr. physicist Étienne-Louis Malus (1775-1812) as a term in optics.

Polish (v.) - c.1300, from O.Fr. poliss-, prp. stem of polir "to polish," from L. polire "to polish, make smooth," of unknown origin. The notion of "to free from coarseness, to refine" first recorded 1340.

Power (n.) - 1297, from Anglo-Fr. pouair, O.Fr. povoir, noun use of the infinitive in O.Fr., "to be able," earlier podir (842), from V.L. *potere, from L. potis "powerful."

Prism - 1570, a type of solid figure, from L.L. prisma (Martianus Capella), from Gk. prisma (Euclid), lit. "something sawed," from prizein "to saw." Meaning in optics is first attested 1612.

Pupil - "center of the eye," 1670 (in L. form from 1398), from O.Fr. pupille (14c.)


Radiation - 15c., from L. radiationem (nom. radiatio), from radiare "to beam, shine," from radius "beam of light" (see radius).

Ray - "beam of light," c.1380, from O.Fr. rai "ray, spoke," from L. radius "ray, spoke, staff, rod." Not common before 17c.; of the sun, usually in reference to heat (beam being preferred for light).

Reflection - c.1380, in reference to both character and surfaces, from L.L. reflexionem, from L. reflex-, pp. stem of reflectere, from re- "back" + flectere "to bend."

Refraction - 1578, from L.L. refractionem "a breaking up," from L. refract-, pp. stem of refringere "break up," from re- "back" + comb. form of frangere "to break."

Resolution - 14c., "process of reducing things into simpler forms," from L. resolutionem (nom. resolutio), from pp. stem of resolvere "loosen." Originally "a breaking into parts;" sense of "solving" (as of mathematical problems) first recorded 1548.

Resonance - mid-15c., from M.Fr. resonance, from L. resonantia "echo," from resonare.

Reticle - From L. reticulum, diminutive of rete, "net." A grid or pattern placed in the eyepiece of an optical instrument, used to establish scale or position.

Retina - 1392, from M.L. retina, probably from V.L. (tunica) *retina, lit. "net-like tunic," on resemblance to the network of blood vessels at the back of the eye, and ult. from L. rete "net."


Saturate (v.) - 1538, probably from adj. (early 15c.), from L. saturatus, pp. of saturare "to fill full, sate, drench," from satur "sated, full," from PIE base *sa- "to satisfy." Originally "satisfy;" meaning "soak thoroughly" first recorded 1756. Saturation bombing first recorded 1942.

Scatter - 12c., possibly a northern Eng. variant of M.E. schateren (see shatter), reflecting.

Scope (1) - "extent," 1534, from It. scopo "aim, purpose, object," from L. scopus, from Gk. skopos "aim, target, watcher," related to skopein "behold, look, consider," skeptesthai "to look at." Originally "mark to shoot at," sense of "distance the mind can reach, extent of view" first recorded c.1600.

Scope (2) - "instrument for viewing," 1872, abstracted from telescope, microscope, etc., from Gk. skopein "to look."

Sensitive - 1392, from M.Fr. sensitif, from M.L. sensitivus "capable of sensation," from L. sensus, pp. of sentire "feel perceive." Meaning "easily affected" first recorded 1816. Sensitize first recorded 1856, originally in photography.

Silhouette - 1798, from Fr. silhouette, in allusion to Etienne de Silhouette (1709-67), Fr. minister of finance in 1759. Probably so called because it was an inexpensive way of making a likeness of someone, a derisive reference to Silhouette's petty economies to finance the Seven Years' War.

Silica - 1801, Mod.L., from L. silex (gen. silicis) "flint, pebble."

Silicon - 1817, coined by British chemist Thomas Thomson from silica, patterned on boron, carbon, etc. Silicone coined 1860s on the same plan. Silicon Valley for the Santa Clara Valley south of San Francisco first attested 1974, from the silicon chips used in computers, watches, etc.

Source - 1346, from O.Fr. sourse "a rising, beginning, fountainhead of a river or stream," fem. noun taken from pp. of sourdre "to rise, spring up," from L. surgere "to rise."

Speckle - 1440, spakle, probably related to O.E. specca "small spot, speck," or from a related M.Du. or M.H.G. word.

Spectrum - 1611, "apparition, specter," from L. spectrum "appearance, image, apparition," from specere "to look at, view." Meaning "band of colors formed from a beam of light" first recorded 1671. Spectroscope is from 1861.

Sphere - restored spelling (early 15c.) of spere (13c.), from O.Fr. espere, from L. sphæra "globe, ball, celestial sphere," from Gk. sphaira "globe, ball."

Stop (v.) - O.E. -stoppian (in forstoppian "to stop up, stifle"), a W.Gmc. borrowing from V.L. *stuppare "to stop or stuff with tow or oakum." Plugs made of tow were used from ancient times in Rhine valley. Sense of "bring or come to a halt" (1440) is from notion of preventing a flow by blocking a hole, and is only in Eng.


Telecentric - From Greek tele-, "far off." The pupil(s) of a system are at infinity.

Telephoto - 1898, shortened form of telephotographic (1892).

Telescope - 1648, from It. telescopio (used by Galileo, 1611), and Mod.L. telescopium (used by Kepler, 1613), both from Gk. teleskopos "far-seeing," from tele- "far" + -skopos "seeing," from skopein "to watch." The verb meaning "to force together one inside the other" (like the sliding tubes of some telescopes) is first recorded 1867.

Toroid – from Gk -oeids, from eidos, "shape, form" and tor(us) to mean a surface generated by a closed curve rotating about, but not intersecting or containing an axis in its own plane.

Transmission - 1611, from L. transmissionem (nom. transmissio) "a sending over or across, passage," from transmissus, pp. of transmittere "send over or across" (see transmit).

Transmit - 14c., from L. transmittere "send across, transfer, pass on," from trans- "across" + mittere "send."

Transparent - early 15c., from M.L. transparentem (nom. transparens), prp. of transparere "show light through," from L. trans- "through" + parere "come in sight, appear." Figurative sense of "easily seen through" is first attested 1592.

Transverse - 1621, from L. transversus "turned or directed across," pp. of transvertere "turn across," from trans- "across" + vertere "to turn."


Vertex - 1570, "the point opposite the base in geometry," from L. vertex "highest point," lit. "the turning point," originally "whirling column, whirlpool," from vertere "to turn." Meaning "highest point of anything" is first attested 1641.

Visible - early 14c., from O.Fr. visible, from L. visibilis "that may be seen," from visus, pp. of videre "to see." Visibility "condition of being seen" is from 1581; meaning "range of vision under given conditions" is from 1914.

Vision - from L. visionem (nom. visio) "sight, thing seen," from pp. stem of videre "to see." The meaning "sense of sight" is first recorded c.1491.

Visual - early 15c., "coming from the eye or sight" (as a beam of light), from L.L. visualis "of sight," from L. visus "sight," from pp. of videre "to see." Meaning "relating to vision" is first attested 1603. The noun meaning "photographic film or other visual display" is first recorded 1951. Visualize is first recorded 1817, said to have been coined by Coleridge.

Vitreous - 1646, from L. vitreus "of glass, glassy," from vitreum "glass."

Vitrify - 1594, from M.Fr. vitrifier, from L. vitrium "glass."

Vitriol - 1392, from O.Fr. vitriol, from M.L. vitriolum "vitriol," from neut. of vitriolus, from L.L. vitreolus "of glass," from L. vitreus "of glass, glassy," from vitrium "glass."


Watt - 1882, in allusion to James Watt (1736-1819), Scottish engineer and inventor.

Wave (n.) - "moving billow of water," 1526, from wave (v.), replacing M.E. waw, from O.E. wagian "to move to and fro" (see wag (v.)). Of people in masses, first recorded 1852; in physics, from 1832.


Xerox - 1952, trademark taken out by Haloid Co. of Rochester, N.Y., for a copying device, from earlier xerography "photographic reduplication without liquid developers" (1948), from Gk. xeros "dry" + -ography as in photography. The verb is first attested 1966, from the noun, despite strenuous objection from the Xerox copyright department.


Zoom – 1886, of echoic origin. Gained popularity c.1917 as aviators began to use it; zoom lens is 1936.

Compiled with help from: Online Etymology Dictionary, Bartleby and OSA Student Chapter Members.

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