A monologue is a long speech by one person. A duologue is a conversation between two persons, as is a dialogue. But dialogue is a much higher frequency word, and it has generalized as well, so that it can also refer loosely to conversations with various numbers of speakers, as well as to the scripts that record actors’ speeches. The -logue spellings are all Standard, but so are those that end in -log, and the use of the latter is increasing. See DIALOGUE; -LOG.
