dark‧ness W3 [uncountable]
when there is no light:
the long hours of darkness during winter
The lamp suddenly went out, leaving us in darkness.
The room was in total darkness.
We lit our campfire as darkness fell (=it became night).
He stared out the window at the gathering darkness (=the night slowly coming).
evil or the devil:
His smooth manner covered a heart of darkness.
the forces/powers of darkness (=the devil or evil people)
the dark quality of a colour:
the darkness of the lenses