early 15c., from Anglo-Fr. defesaunce, O.Fr. defesance "undoing, destruction," from O.Fr. defesant, prp. of desfaire (Mod.Fr. défaire) "to undo, destroy," from des- (see
dis-) + faire "to do" (from L. facere; see
factitious). Related: Defease (late 15c.); defeasible (1580s).