The Collaborative International Dictionary of English v.0.48:

Monophonic \Mon`o*phon"ic\, a. [Mono- + Gr. ? a voice.]
   1. (Mus.) Single-voiced; having but one part; as, a
      monophonic composition; -- opposed to polyphonic.
      [1913 Webster]

   2. Of or relating to a system for recording and reproducing
      sound, which has only one sound channel; also called
      monaural or mono. It contrasts with stereophonic (or
      stereo), quadraphonic, or surround-sound, which have
      two or more channels, and can thus reproduce the effect of
      the sound coming from more than one direction.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

monaural \mon*au"ral\ (m[o^]n*[^o]r"al), a.
   1. Having or hearing with only one ear.
      [PJC]

   2. Same as monophonic[2].
      [PJC]

WordNet (r) 3.0 (2006):

monaural
    adj 1: relating to or having or hearing with only one ear;
           "monaural deafness" [ant: biaural, binaural]