The Collaborative International Dictionary of English v.0.48:

Monologue \Mon"o*logue\, n. [F. monologue, Gr. ? speaking alone;
   mo`nos alone, single, sole + lo`gos speech, discourse,
   le`gein to speak. See Legend.]
   1. A speech uttered by a person alone; soliloquy; also, talk
      or discourse in company, in the strain of a soliloquy; as,
      an account in monologue. --Dryden.
      [1913 Webster]

   2. A dramatic composition for a single performer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

monologue
    n 1: speech you make to yourself [syn: soliloquy, monologue]
    2: a long utterance by one person (especially one that prevents
       others from participating in the conversation)
    3: a (usually long) dramatic speech by a single actor

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "monologue":
   Grand Guignol, Passion play, Tom show, antimasque, aside,
   audience success, ballet, bomb, broadcast drama, burlesque show,
   charade, cliff hanger, clockwork regularity, closet drama,
   comedy drama, constancy, critical success, daily round,
   daytime serial, dialogue, dingdong, documentary drama, drama,
   dramalogue, dramatic play, dramatic series, drone, duodrama,
   duologue, epic theater, even pace, even tenor,
   experimental theater, extravaganza, failure, flop, gasser,
   giveaway, happening, hit, hit show, improvisational drama,
   invariability, legitimate drama, masque, melodrama, minstrel show,
   miracle, miracle play, monodrama, monology, monotone,
   monotonousness, monotony, morality, morality play, music drama,
   musical revue, mystery, mystery play, opera, orderliness, pageant,
   panel show, pantomime, pastoral, pastoral drama, piece, play,
   playlet, problem play, psychodrama, quiz show, radio drama,
   regularity, review, revue, sameliness, sameness, sensational play,
   serial, show, singsong, sitcom, situation comedy, sketch, skit,
   smoothness, soap, soap opera, sociodrama, soliloquy, solo,
   spectacle, stage play, stage show, straight drama, success,
   suspense drama, tableau, tableau vivant, talk show, teleplay,
   television drama, television play, theater of cruelty,
   total theater, treadmill, undeviation, undifferentiation,
   unvariation, variety show, vaudeville, vaudeville show, vehicle,
   word-of-mouth success, work