Source : Webster's Revised Unabridged Dictionary (1913)

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.

   {Heterologous stimulus}. (Physiol.) See under {Stimulus}.

   {Heterologous tumor} (Med.), a tumor differing in structure
      from the normal tissues of the body.

Source : WordNet®

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