c.1300, "misdeed," from Old French 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). Translating Medieval Latin foris factum. Sense shifted mid-15c. from the crime to the penalty: "something to which the right is lost through a misdeed." As an adjective from late 14c., from Old French forfait.
c.1300, "to lose by misconduct;" see forfeit (n.). Related: Forfeited; forfeiting.