Nightfall definition: the coming of night; the end of daylight; dusk.. See examples of NIGHTFALL used in a sentence. A nightfall, known scientifically as a nocturnal emission, and also informally known as a wet dream, sex dream, or sleep orgasm, is a spontaneous orgasm that involves ejaculation for males and vaginal wetness or an orgasm (or both) for females during sleep. Nightfall is the part of a day when the sun goes down and evening begins. In suburban neighborhoods, parents often call their kids to come home for dinner at nightfall. / ˈnɑɪtˌfɔl / Add to word list the time at the end of the day when it becomes dark (Definition of nightfall from the Cambridge Academic Content Dictionary © Cambridge University Press)
