Proto-Indo-European root meaning "to see."
It forms all or part of: amblyopia; antique; antler; atrocity; autopsy; binocle; binocular; biopsy; catoptric; Cyclops; daisy; enoptomancy; eye; eyelet; ferocity; hyperopia; inoculate; inveigle; monocle; monocular; myopia; necropsy; ocular; oculist; oculus; oeillade; ogle; ophthalmo-; optic; optician; optics; optometry; panoptic; panopticon; Peloponnesus; pinochle; presbyopia; prosopopeia; stereoptican; synopsis; triceratops; ullage; wall-eyed; window.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit akshi "the eye; the number two," Greek osse "(two) eyes," opsis "a sight;" Old Church Slavonic oko, Lithuanian akis, Latin oculus, Greek okkos, Tocharian ak, ek, Armenian akn "eye."
1811, "develop polarization in," in optics, from French polariser, coined by French physicist Étienne-Louis Malus (1775-1812) as a term in optics, from Modern Latin polaris "polar" (see polar). Transferred sense of "to accentuate a division in a group or system" is recorded from 1949 in Arthur Koestler. Related: Polarized; polarizing.
1803, in optics, "to break up (a beam of light) by deflecting it from a right line," perhaps a back-formation from diffraction. In acoustics by 1825. Related: Diffracted; diffracting.
late 14c., perspectif, "the science of optics," from Old French perspective and directly from Medieval Latin perspectiva ars "science of optics," from fem. of perspectivus "of sight, optical" from Latin perspectus "clearly perceived," past participle of perspicere "inspect, look through, look closely at," from per "through" (from PIE root *per- (1) "forward," hence "through") + specere "look at" (from PIE root *spek- "to observe"). The English word is also attested from early 15c. as an adjective, "pertaining to the science of optics."
The sense of "the art of drawing solid objects on a flat surface so as to give appearance of distance or depth" is attested by 1590s, probably by influence of Italian prospettiva, an artists' term. The meaning "proper or just proportion, appropriate relation in the mind of the parts of a subject to one another" is recorded by c. 1600, hence the figurative meaning "mental outlook over time" (1762).
1775 in optics, "bring into focus" (transitive); 1807 in the figurative sense, from focus (n.). Intransitive use by 1864, originally in photography. Related: Focused; focusing; less commonly focussed; focussing.
in optics, "point or object from which light radiates," 1714; see radiant (adj.). In astronomy, of meteor showers, "the point in the heavens from which the shooting stars seem to proceed," by 1834, in reference to the great shower of the previous November.
in optics, "the spreading of light or deflection of its rays," 1670s, from French diffraction (17c.) or directly from Modern Latin diffractionem (nominative diffractio), noun of action from past-participle stem of Latin diffringere "break apart in pieces," from dis- "apart" (see dis-) + frangere "to break" (from PIE root *bhreg- "to break").
1560s, "relating to or connected with the science of optics; pertaining to vision," from optic + -al (1). Of abstract art, from 1964. In astronomy, in reference to double stars that appear so only because they lie in the same line of sight from earth, by 1868. Optical illusion is attested by 1757. Related: Optically.