Is it farther or further?
early 13c., "literary work consisting of a conversation between two or more persons," from Old French dialoge, from Latin dialogus, from Greek dialogos "conversation, dialogue," related to dialogesthai "converse," from dia- "across" (see dia-) + legein "speak" (see lecture (n.)).
Sense broadened to "a conversation" c.1400. Mistaken belief that it can only mean "conversation between two persons" is from confusion of dia- and di- (1). A word for "conversation between two persons" is the hybrid duologue (1864).
in its widest sense, the recorded conversation of two or more persons, especially as an element of drama or fiction. As a literary form, it is a carefully organized exposition, by means of invented conversation, of contrasting philosophical or intellectual attitudes. The oldest known dialogues are the Sicilian mimes, written in rhythmic prose by Sophron of Syracuse in the early 5th century BC. Although none of these has survived, Plato knew and admired them. But the form of philosophic dialogue that he perfected by 400 BC was sufficiently original to be an independent literary creation. With due attention to characterization and the dramatic situation from which the discussion arises, it develops dialectically the main tenets of Platonic philosophy. To Lucian in the 2nd century AD the dialogue owes a new tone and function. His influential Dialogues of the Dead, with their coolly satirical tone, inspired innumerable imitations in England and France during the 17th and 18th centuries, e.g., dialogues by the French writers Bernard de Fontenelle (1683) and Francois Fenelon (1700-12).