Appeared in the sixteenth century, probably from a Scandinavian source meaning 'spray' — deeper etymology uncertain.
A thick cloud of tiny water droplets suspended in the atmosphere at or near the earth's surface, reducing visibility.
Probably from a Scandinavian source akin to Danish "fog" ("spray, shower, snowdrift") and Norwegian "foka" ("to spray, to drift"), related to Old Norse "fjúk" ("snowdrift, blizzard"), from Proto-Germanic *feukaz ("to blow, to drift"). The Proto-Germanic form traces to PIE *pewg- ("to blow, to puff"), which also appears in Lithuanian "pūgà" ("snowstorm, blizzard"). The word is notably absent from Old English — "mist" and "þēostra" served instead — and first appears in Middle English around the 14th century, likely
The word 'smog' was coined in 1905 by the London public health official Henry Antoine Des Voeux, who blended 'smoke' + 'fog' to describe London's notorious industrial foul air. London's 'pea-soupers' — thick yellow-green smogs caused by coal burning — killed thousands: the Great Smog of 1952 caused an estimated 4,000–12,000 deaths and directly led to the Clean Air Act 1956.