WordNet (r) 3.0 (2006):

duologue
    n 1: a conversation between two persons [syn: dialogue,
         dialog, duologue]
    2: a part of the script in which the speaking roles are limited
       to two actors

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "duologue":
   Grand Guignol, Passion play, Tom show, antimasque,
   audience success, ballet, bomb, broadcast drama, bull session,
   burlesque show, charade, chinfest, cliff hanger, closet drama,
   comedy drama, confab, confabulation, critical success,
   daytime serial, dialogue, documentary drama, drama, dramalogue,
   dramatic play, dramatic series, duodrama, epic theater,
   experimental theater, extravaganza, failure, flop, gasser,
   giveaway, happening, hit, hit show, improvisational drama,
   legitimate drama, masque, melodrama, minstrel show, miracle,
   miracle play, monodrama, monologue, morality, morality play,
   music drama, musical revue, mystery, mystery play, opera, pageant,
   palaver, panel show, pantomime, pastoral, pastoral drama, piece,
   play, playlet, problem play, psychodrama,
   question-and-answer session, quiz show, radio drama, review, revue,
   sensational play, serial, show, sitcom, situation comedy, sketch,
   skit, soap, soap opera, sociodrama, spectacle, speech, stage play,
   stage show, straight drama, success, suspense drama, tableau,
   tableau vivant, talk, talk show, talkfest, teleplay,
   television drama, television play, theater of cruelty,
   total theater, trialogue, variety show, vaudeville,
   vaudeville show, vehicle, word-of-mouth success, words, work