fog
n. C / Un. a thick cloud of very small water drops in the air near the ground. It makes it very difficult to see clearly when you are driving or walking.
n. a thick cloud of water droplets suspended in the atmosphere at or near the earth's surface that obscures or restricts visibility.
The thick fog makes it hard to see the road.
Heavy fog delayed several flights this morning because the pilots could not see the runway clearly enough to land.
As the sun began to rise, a dense blanket of fog rolled in from the coast, swallowing the lighthouse and reducing the visibility to less than ten meters.
Origin uncertain; but probably of North Germanic origin. Probably either a back-formation from foggy (“covered with tall grass; thick, marshy”), from the earlier-attested fog (“tall grass”) (see below), or from or related to Danish fog (“spray, shower, drift, storm”), related to Icelandic fok (“spray, any light thing tossed by the wind, snowdrift”), Icelandic fjúka (“to blow, drive”), from Proto-Germanic feukaną (“to whisk, blow”), from Proto-Indo-European pug- (“billow, bulge, drift”), from pew-, pow- (“to blow, drift, billow”), in which case related to German fauchen (“to hiss, spit, spray”).
From Middle English fogge (“tall grass”), probably from Norwegian fogg (“tall, worthless grass”); compare Scots fog (“moss; lichen”).
Compare Old Dutch focker.
Uncountable when referring to the weather condition in general; countable when referring to specific instances or types of fog.