1. (n.) The absence of correspondence, or relation, in type of structure; lack of analogy between parts, owing to their being composed of different elements, or of like elements in different proportions; variation in structure from the normal form; -- opposed to homology.

2. (n.) The connection or relation of bodies which have partial identity of composition, but different characteristics and properties; the relation existing between derivatives of the same substance, or of the analogous members of different series; as, ethane, ethyl alcohol, acetic aldehyde, and acetic acid are in heterology with each other, though each in at the same time a member of a distinct homologous series. Cf. Homology.