foolhardy

From Middle English folehardy, foolhardi, folherdi, from Old French fol hardi (“foolishly bold”), from Old French fol (“foolish, silly; insane, mad”) (from Latin follis (“bellows; purse, sack; inflated ball; belly, paunch”), ultimately from Proto-Indo-European bʰelǵʰ- (“to swell”)) + Old French hardi (“durable, hardy, tough”) (past tense of hardir (“to harden”), from the unattested Frankish hartjan, from Proto-Germanic *harduz (“hard; brave”)), equivalent to fool + hardy. Compare fool-bold, fool-large, etc.