nightfall
n. uncountable B2 Upper Intermediate US //ˈnaɪtˌfɔɫ// UK //nˈaɪtfɔːl// night·fall
n. the time of day when it starts to get dark and night begins.
n. the onset of darkness at the end of the day; the transition from twilight to night.
We should try to reach the camp before nightfall.
The hikers quickened their pace as nightfall approached, hoping to find the trail marker before the light faded completely.
The ancient city gates were traditionally locked at nightfall to protect the inhabitants from nocturnal threats, a practice that continued well into the nineteenth century.
From night + fall. Cf. dewfall.
Usage
Often follows the preposition 'at' or 'before'.