Of twilight; active or occurring chiefly at dawn and dusk, when the world is neither day nor night and edges soften into uncertainty (scientific; also literary). Crepuscular belongs to thresholds, the hour when light hesitates.

From Latin crepusculum “twilight,” a diminutive suggesting a smaller, gentler dark. The word carries the feeling of that time: not blackness, but a dimming that makes familiar things strange.