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 "to make, do," from PIE root *dhe- "to set, put"). 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.
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.