noun

a thick cloud of tiny water droplets suspended in the atmosphere at or near the earth’s surface which obscures or restricts visibility (to a greater extent than mist; strictly, reducing visibility to below 1 km).

the collision occurred in thick fog

mist,mistiness,fogginess,haar,smog,murk,murkiness,haze,haziness,gloom,gloominess,pea-souper,(sea) fret,clag,brume,fume

verb

(with reference to a glass surface) cover or become covered with steam.

hot steam drifted about her, fogging up the window

steam up,mist over,cloud over,film over,become misty,become blurred,become covered in condensation,make hazy,make cloudy,obscure,shade,veil,befog,becloud