eye (n.)

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."

"discoloration around the eye from injury" c. 1600, from black (adj.) + eye (n.). Figurative sense of "injury to pride, rebuff" is by 1744; that of "bad reputation" is from 1880s.

In reference to dark eyes, often as a mark of beauty, from 1660s. Black-eyed is from 1590s of women, of peas from 1728. The black-eyed Susan as a flower (various species) so called from 1881, for its appearance. It also was the title of a poem by John Gay (1685-1732), which led to a popular mid-19c. British stage play of the same name.

All in the Downs the fleet was moored,

  The streamers waving in the wind,

When black-eyed Susan came aboard,

  "Oh! where shall I my true love find?

Tell me, ye jovial sailors, tell me true,

If my sweet William sails among the crew?"

[etc.]