Real Dictionary

fog
singular noun: A fog is an unpleasant cloud of something such as smoke inside a building or room.
variable noun: When there is fog, there are tiny drops of water in the air which form a thick cloud and make it difficult to see things.

fog in American English 1
a large mass of water vapor condensed to fine particles, at or just above the earth's surface; thick, obscuring mist
to become surrounded or covered by fog
to surround or cover with fog
intransitive verb: to become enveloped or obscured with or as if with fog
noun: a cloudlike mass or layer of minute water droplets or ice crystals near the surface of the earth, appreciably reducing visibility
transitive verb: to cover or envelop with or as if with fog

fog in American English 2
a new growth of grass after cutting or grazing
noun: a second growth of grass, as after mowing

fog in British English 1
noun: a mass of droplets of condensed water vapour suspended in the air, often greatly reducing visibility, corresponding to a cloud but at a lower level
verb: to envelop or become enveloped with or as if with fog

fog in British English 2
noun: a second growth of grass after the first mowing