n. The quality of being homologous; correspondence; relation.n. 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.n. 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; , all members of the paraffin series. In an extended sense, the term is applied to the relation between chemical elements of the same group. Cf. Heterology.