c. 1300, "something seen in the imagination or in the supernatural," from Anglo-French visioun, Old French vision "presence, sight; view, look, appearance; dream, supernatural sight" (12c.), from Latin visionem (nominative visio) "act of seeing, sight, thing seen," noun of action from past participle stem of videre "to see," from PIE root *weid- "to see." The meaning "sense of sight" is first recorded late 15c. Meaning "statesman-like foresight, political sagacity" is attested from 1926.
"light from the sky when the sun is below the horizon at morning and evening," late 14c. (twilighting), a compound of twi- + light (n.) Cognate with Middle Flemish twilicht, Dutch tweelicht (16c.), Middle High German twelicht, German zwielicht. Exact connotation of twi- in this word is unclear, but it appears to refer to "half" light, rather than the fact that twilight occurs twice a day. Compare also Sanskrit samdhya "twilight," literally "a holding together, junction," Middle High German zwischerliecht, literally "tweenlight." Originally and most commonly in English with reference to evening twilight but occasionally used of morning twilight (a sense first attested mid-15c.). Figurative extension recorded from c. 1600.
Twilight zone is from 1901 in a literal sense, a part of the sky lit by twilight; from 1909 in extended senses in references to topics or cases where authority or behavior is unclear. In the 1909 novel "In the Twilight Zone," the reference is to mulatto heritage. "She was in the twilight zone between the races where each might claim her ...." The U.S. TV series of that name is from 1959.
figurative use, "dim, indistinct," is attested from 1660s; literal use, "pertaining to or resembling twilight," from 1755, from Latin crepusculum "twilight, dusk," related to creper "obscure, uncertain," from Proto-Italic *krepos "twilight," which is of uncertain origin. It is not certain whether "twilight" or "obscure" was the original sense; de Vaan writes, "there is no known root of the form *krep- from which the extant meanings can be derived."
Especially of evening twilight, but 17c.-18c. also "like morning twilight" as symbolic of imperfect enlightenment. In zoology, "flying or appearing at sunset," from 1826. An older (and lovelier-sounding) adjective form was crepusculine (1540s).
"morning or evening twilight," late 14c., from Old French crépuscule (13c.), from Latin crepusculum.
1909 in the figurative sense of "complete overthrow" of something; from German Götterdämmerung (18c.), literally "twilight of the gods," from genitive plural of Gott "god" (see god) + Dämmerung "dusk, twilight," from PIE root *teme- "dark" (see temerity). Used by Wagner as the title of the last opera in the Ring cycle. It translates Old Norse ragna rok "the doom or destruction of the gods, the last day, world's end." A better transliteration is Goetterdaemmerung.
Old English glomung "twilight, the fall of evening," found but once (glossing Latin crepusculum), and formed (probably on model of æfning "evening") from glom "twilight," which is related to glowan "to glow" (hence "glow of sunrise or sunset"), from Proto-Germanic *glo- (see glow (v.)). Fell from currency except in Yorkshire dialect, but preserved in Scotland and reintroduced by Burns and other Scottish writers after 1785.