Source : Webster's Revised Unabridged Dictionary (1913)

Homologous \Ho*mol"o*gous\, a. [Gr. ? assenting, agreeing; ? the
   same + ? speech, discourse, proportion, ? to say, speak.]
   Having the same relative position, proportion, value, or
   structure. Especially:
   (a) (Geom.) Corresponding in relative position and
       proportion.

             In similar polygons, the corresponding sides,
             angles, diagonals, etc., are homologous. --Davies &
                                                  Peck (Math.
                                                  Dict.).
   (b) (Alg.) Having the same relative proportion or value, as
       the two antecedents or the two consequents of a
       proportion.
   (c) (Chem.) Characterized by homology; belonging to the same
       type or series; corresponding in composition and
       properties. See {Homology}, 3.
   (d) (Biol.) Being of the same typical structure; having like
       relations to a fundamental type to structure; as, those
       bones in the hand of man and the fore foot of a horse are
       homologous that correspond in their structural relations,
       that is, in their relations to the type structure of the
       fore limb in vertebrates.

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

Source : WordNet®

homologous
     adj 1: having the same evolutionary origin but serving different
            functions; "the wing of a bat and the arm of a man are
            homologous" [ant: {analogous}, {heterologous}]
     2: corresponding or similar in position or structure or
        function or characteristics; especially derived from an
        organism of the same species; "a homologous tissue graft"
        [ant: {heterologous}, {autologous}]