when there is no light, especially because the sun has gone down:
my childish fear of the dark
in the dark
I turned off the light and lay there in the dark.
We stood outside in the pitch dark (=when there is no light at all).
after, before, or until the sun goes down at night:
I want you home before dark.
knowing nothing about something important, because you have not been told about it:
in the darkinformal
We're in the dark just as much as you are.
College officials were kept in the dark about the investigation.