1590s, legal Latin, "law of retaliation," an eye for an eye, a tooth for a tooth, from lex "law" (see legal) + talionis, genitive of talio "exaction of payment in kind" (see retaliation). Not related to talon. Other legal Latin phrases include lex domicilii "the law of the place where the person resides," lex fori "law of the place in which an action is brought."