Foggy means with thick low cloud hiding everything around you. A foggy morning, foggy conditions, foggy glasses.
Fog is cloud at ground level, and the difference from mist is only visibility — under a kilometre and it is fog. Not the foggiest means no idea at all. Note that the word may be older than fog itself, which may be a back-formation from it.
1adjectivefoggyWith thick low cloud hiding everything around.
“It was so foggy this morning that I couldn't see the end of the street.”
foggy is a quality of weather.
Also accepted in games: misty
Fog plus -y. The adjective may be older than the noun, and fog may be a back-formation from foggy.
Proto-Indo-European
*pug- — billow, bulge, drift
Proto-Germanic
*feukaną — to whisk, blow
Danish
fog — spray, shower, drift, storm
English
fog
English, today
foggy
Built from
From fog + y, originally in the sense "covered with tall grass; marshy; thick". It is not clear whether fog (“mist”) is a back-formation from foggy (“covered with tall, obscuring grass”) or has a separate Germanic origin, and hence whether foggy (“covered with tall grass”) and foggy (“obscured by mist”) represent one word or two. See fog ("mist"; "tall grass") for more. fog Origin unknown; but probably of gmq 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”).
Etymology from Wiktionary, CC BY-SA