'Nighttime' definitions:

Definition of 'nighttime'

From: WordNet
noun
The time after sunset and before sunrise while it is dark outside [syn: night, nighttime, dark] [ant: day, daylight, daytime]

Definition of 'Nighttime'

From: GCIDE
  • Nighttime \Night"time`\, n. The time from dusk to dawn; -- opposed to daytime. [1913 Webster]