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Origin unknown; possibly a variant of frowsy (frousy, frouzy, frowzy), etymology also unknown; and possibly related to Old French frouste (“decayed, in a state of ruin”). Compare also froughy, frow.
Etymology from Wiktionary, CC BY-SA 4.0.
frowsty
Today it means: Of an atmosphere: not fresh; close, musty, stuffy; of an object: having a musty, stale odour. Full definition →