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The early Romans had two words for the twilight. Crepusculum was favored by Roman writers for the half-light of evening, just after the sun sets; it is a diminutive formation based on their word for "dusky," which is creper. Diluculum was reserved for morning twilight, just before the sun rises—it is related to lucidus, meaning "bright." We didn't embrace either of these Latin nouns as substitutes for our Middle English twilight, but we did form the adjective crepuscular in the 17th century. At first, it only meant "dim" or "indistinct," often used in a figurative sense. In the 1820s, we added its special zoological sense, describing animals that are most active at twilight.

Examples

"After dinner they went out on the terrace for a look at the moon-misted park. Through the crepuscular whiteness the trees hung in blotted masses." — Edith Wharton, The Reef, 1912

"Rabbits are crepuscular feeders, which means they tend to leave their burrows in the twilight hours around sunset and sunrise to eat." — Joan Morris, The Mercury News (California), 24 Aug. 2016