Crepuscular
Etymology
From Latin "crepusculum" ("twilight, dusk"), from "creper" ("dusky, dark, obscure"). English adopted it for the dim light of both dawn and dusk, and naturalists later extended it to creatures that are active at those in-between hours.
adjective · /krih-PUS-kyuh-lur/
Relating to or resembling twilight; dim.
What it names
The word for the half-light of dusk or dawn — and for the animals, like bats and moths, that stir in it.
Example
In the crepuscular light before dawn, the deer crept out to feed.
Related idea
Vespertine refers specifically to the evening; crepuscular covers the dim light of both dusk and dawn.
adjective · /krih-PUS-kyuh-lur/
Of an animal, active mainly at dawn and dusk rather than by day or night.
What it names
The daily activity pattern of creatures such as deer, rabbits, and many moths that stir in the low light of twilight.
Example
Deer are crepuscular, which is why so many collisions happen at dusk.
Related idea
This zoological sense sits beside diurnal (active by day) and nocturnal (active by night), and shares the twilight image of the general sense — the Latin crepusculum, "dusk."