late 14c., replien, "respond verbally, make an answer; make opposition, retaliate," from Old French replier "to reply, turn back," from Late Latin replicare "to reply, repeat," in classical Latin "fold back, fold over, bend back," from re- "back, again" (see re-) + plicare "to fold" (from PIE root *plek- "to plait"). Latin literal sense of "to fold back" is attested from early 15c. in English but is not now used. Modern French répliquer (Middle French replier) is directly from Late Latin. Related: Replied; replying.