The Collaborative International Dictionary of English v.0.48:

Homophonic \Ho`mo*phon"ic\, Homophonous \Ho*moph"o*nous\, a.
   [Gr. ?; ? the same + ? sound, tone: cf. F. homophone.]
   1. (Mus.)
      (a) Originally, sounding alike; of the same pitch;
          unisonous; monodic.
      (b) Now used for plain harmony, note against note, as
          opposed to polyphonic harmony, in which the several
          parts move independently, each with its own melody.
          [1913 Webster]

   2. Expressing the same sound by a different combination of
      letters; as, bay and bey.
      [1913 Webster]

WordNet (r) 3.0 (2006):

homophonic
    adj 1: having the same sound
    2: having a single melodic line with accompaniment