dusk

Dusk comes from Middle English dosk or duske, meaning "dusky," from Old English dox ("dark, swarthy"), tracing back to Proto-Germanic *duskaz ("dark, smoky") and ultimately Proto-Indo-European *dʰwes-, tied to a root meaning smoke, mist, or haze.

It began as an adjective describing something dark or swarthy in color, and later settled into English as the noun we use for the dimming light between day and night.

It's a cognate of Latin fuscus ("dark, dusky") and shares deeper roots with dye, dust, and dun — words all touched by that old sense of smoke and shadow. It's also a doublet of fuscous.