The Collaborative International Dictionary of English v.0.48:

Homology \Ho*mol"o*gy\, n. [Gr. ? agreement. See Homologous.]
   1. The quality of being homologous; correspondence; relation;
      as, the homologyof similar polygons.
      [1913 Webster]

   2. (Biol.) Correspondence or relation in type of structure in
      contradistinction to similarity of function; as, the
      relation in structure between the leg and arm of a man; or
      that between the arm of a man, the fore leg of a horse,
      the wing of a bird, and the fin of a fish, all these
      organs being modifications of one type of structure.
      [1913 Webster]

   Note: Homology indicates genetic relationship, and according
         to Haeckel special homology should be defined in terms
         of identity of embryonic origin. See Homotypy, and
         Homogeny.
         [1913 Webster]

   3. (Chem.) The correspondence or resemblance of substances
      belonging to the same type or series; a similarity of
      composition varying by a small, regular difference, and
      usually attended by a regular variation in physical
      properties; as, there is an homology between methane,
      CH4, ethane, C2H6, propane, C3H8, etc., all members
      of the paraffin series. In an extended sense, the term is
      applied to the relation between chemical elements of the
      same group; as, chlorine, bromine, and iodine are said to
      be in homology with each other. Cf. Heterology.
      [1913 Webster]

   General homology (Biol.), the higher relation which a
      series of parts, or a single part, bears to the
      fundamental or general type on which the group is
      constituted. --Owen.

   Serial homology (Biol.), representative or repetitive
      relation in the segments of the same organism, -- as in
      the lobster, where the parts follow each other in a
      straight line or series. --Owen. See Homotypy.

   Special homology (Biol.), the correspondence of a part or
      organ with those of a different animal, as determined by
      relative position and connection. --Owen.
      [1913 Webster]