出典:Wiktionary
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.
foolhardy (comparative foolhardier または more foolhardy, superlative foolhardiest または most foolhardy)