fog

The origin of "fog" is uncertain, but it's probably of North Germanic descent. It may be a back-formation from "foggy" (covered with tall, marshy grass), itself from Middle English "fogge" (tall grass), likely from Norwegian "fogg" (tall, worthless grass); or it may instead trace to Danish "fog" (spray, shower, drift, storm), related to Icelandic "fok" and "fjúka" (to blow, drive), from Proto-Germanic "*feukaną" (to whisk, blow).

One proposed path runs from grass to grassy dampness to the mist that clings to such ground; the other runs from windblown spray straight to the drifting haze we now call fog.

If the wind-and-spray theory is correct, "fog" is kin to German "fauchen" (to hiss, spit, spray), both descending from a root meaning to blow or billow.