c. 1200, "literary work consisting of a conversation between two or more persons," from Old French dialoge and directly from Latin dialogus, from Greek dialogos "conversation, dialogue," related to dialogesthai "converse," from dia "across, between" (see dia-) + legein "speak," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')."

Sense extended by c. 1400 to "a conversation between two or more persons." The mistaken belief that it can mean only "conversation between two persons" is from confusion of dia- and di- (1); the error goes back to at least 1532, when trialogue was coined needlessly for "a conversation between three persons." A word that has been used for "conversation between two persons" and cannot mean otherwise is the hybrid duologue (1864).