From Greek terms meaning "one word" or "one person," monologue refers to a speech by one person. In drama, monologue applies to a form of entertainment by a single speaker or to an extended part of the text of a play uttered by an actor or actress. Monologue is sometimes used disparagingly to refer to the comments of someone who talks glibly and incessantly: "Several of the most moving passages in Hamlet are the monologues delivered by leading characters." "It's impossible to have a conversation with him because all he does is talk in monologue." Dialogue, from Greek words meaning "two words" or "two speeches," refers to conversation between two or more persons. Dialogue is a currently popular term for an exchange of ideas on such issues as politics, human rights, economics, and religion: "The managers and workers in this plant should have a dialogue about their common problems."
Dictionary of problem words and expressions. Harry Shaw. 1975.