cloud noun [uncountable and countable] a white or grey mass in the sky that forms from very small drops of water:
The storm was still a way off but black clouds were gathering. Thick cloud obscured the top of the hill.fog noun [uncountable and countable] very thick cloud near the ground which is difficult to see through:
The cars crashed into each other in thick fog. The fog had lifted (=disappeared)slightly.mist noun [uncountable and countable] light cloud near the ground that makes it difficult for you to see very far.
Mist is usually not as thick as
fog. You often get mist near areas of water or mountains:
The morning mist was lifting and the sun was coming up. A grey mist hung over the water. The hills were shrouded in mist (=surrounded by mist).haze noun [singular, uncountable] smoke, dust, or mist in the air which is difficult to see through:
He saw the horses coming towards him through a haze of dust. The road shimmered in the heat haze. A pale blue haze hung over the far-off mountains.smog noun [uncountable and countable] dirty air that looks like a mixture of smoke and fog, caused by smoke from cars and factories in cities:
The city is covered in smog for much of the year. A smog warning was issued for parts of Southern Oregon.thundercloud noun [countable] a large dark cloud that you see before or during a storm:
He watched the thunderclouds roll across the valley.vapour trail British English,
vapor trail American English noun [countable] the white line that is left in the sky by a plane:
High overhead, a jet left its vapour trail across the blue sky. [TahlilGaran] English Thesaurus ▲