The Collaborative International Dictionary of English v.0.48:

Heterologous \Het`er*ol"o*gous\, a. [Hetero- + Gr. ?
   proportion.]
   Characterized by heterology; consisting of different
   elements, or of like elements in different proportions;
   different; -- opposed to homologous; as, heterologous organs.
   [1913 Webster]

   Heterologous stimulus. (Physiol.) See under Stimulus.

   Heterologous tumor (Med.), a tumor differing in structure
      from the normal tissues of the body.
      [1913 Webster]

WordNet (r) 3.0 (2006):

heterologous
    adj 1: not corresponding in structure or evolutionary origin
           [syn: heterologous, heterologic, heterological]
           [ant: analogous, homologous]
    2: derived from organisms of a different but related species; "a
       heterologous graft" [ant: autologous, homologous]