1 [countable/uncountable] a thick cloud that forms close to the ground or to water and is difficult to see through. Fog is thicker than mist
a patch of fog:
There may be some patches of fog around dawn.
a blanket of fog (=fog that covers everything):
a thick blanket of fog in the valley
fog lifts (=goes away):
We’ll leave when this fog has lifted.
Synonyms and related words