1660s, "long speech by one person, scene in a drama in which a person speaks by himself," from French monologue, from Late Greek monologos "speaking alone or to oneself," from Greek monos "single, alone" (from PIE root *men- (4) "small, isolated") + logos "speech, word," from legein "to speak," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Related: Monologist.
"to make a speech," especially a grandiloquent one, c. 1600, a colloquial back-formation from peroration (q.v.), or else from Latin peroratus, past participle of perorare. Related: Perorated; perorating.