forfeityoudaoicibaDictYouDict[forfeit 词源字典]
forfeit: [13] A forfeit was originally a ‘transgression’ or ‘misdemeanour’. The word comes from Old French forfet, a derivative of the verb forfaire or forsfaire ‘commit a crime’. This was a compound formed from fors- ‘beyond (what is permitted or legal)’, which is descended from Latin forīs ‘outdoor, outside’ (source of English forest and related to foreign), and faire ‘do, act’, which came from Latin facere (whence English fact, fashion, feature, etc).

The etymological meaning ‘misdeed’ was originally taken over from Old French into Middle English (‘Peter was in hand nummen [taken] for forfait he had done’, Cursor mundi 1300), but by the 15th century it was being edged out by ‘penalty imposed for committing such a misdeed’.
=> door, fact, factory, fashion, forest, foreign[forfeit etymology, forfeit origin, 英语词源]
forfeit (n.)youdaoicibaDictYouDict
late 14c., forfet, "misdeed, offense against established authority," also "something to which the right is lost through a misdeed," from Old French forfet, forfait "crime, punishable offense" (12c.), originally past participle of forfaire "transgress," from for- "outside, beyond" (from Latin foris; see foreign) + faire "to do" (from Latin facere; see factitious). A French version of Medieval Latin foris factum; the notion perhaps is to "do too much, go beyond (what is right)." As an adjective from late 14c., from Old French forfait. Compare foreclose.
forfeit (v.)youdaoicibaDictYouDict
mid-14c., " transgress, offend, misbehave;" late 14c., "to lose by misconduct," from forfeit (n.) or from Anglo-French forfet, Old French forfait, past participle of forfaire. Related: Forfeited; forfeits; forfeiting.