having the same or a similar relation; corresponding, as in relative position or structure.

corresponding in structure and in origin, but not necessarily in function

The wing of a bird and the foreleg of a horse are homologous.

having the same alleles or genes in the same order of arrangement

homologous chromosomes.

Chemistry . of the same chemical type, but differing by a fixed increment of an atom or a constant group of atoms

Methyl and ethyl alcohols are homologous.

Immunology . pertaining to an antigen and its specific antibody.