noun

1. Biol. a similarity in appearance or structure of organisms belonging to different species or races
2. Chem. an identity or close similarity in the crystalline form of substances usually containing different elements but having similar composition
3. Math. a one-to-one correspondence between two mathematical systems, sets, etc. that preserves the basic operations, as the correspondence between binary numbers and decimal numbers, each a set of real numbers

Etymology: < isomorphic + -ism