crepuscular (adjective) –
1 : of, relating to, or resembling twilight
2 : occurring or active during twilight
Source : Online Etymology Dictionary
Etymology : 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.” In zoology, “flying or appearing at sunset,”; from 1826.
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