Technical term in crystallography: different substances crystallizing in the same or closely similar form.
Calcite and magnesite are in an isomorphic relationship.
Technical term in genetics: similarity of form or structure between organisms of different species or between different parts of the same organism.
Isomorphic genes can have similar functions even in different species.
Compound of 異種 (different kind) and 同形 (same form). The exact historical derivation is uncertain; the term is used as a technical translation equivalent for 'isomorphism' in crystallography and genetics.