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