“The word ‘isomorphism’ applies when two complex structures can be mapped onto each other, in such a way that to each part of one structure there is a corresponding part in the other structure, where ‘corresponding’ means that the two part play similar roles in their respective structures.”
— Douglas R. Hofstadter, author of several notable books including Gödel, Escher, Bach: An Eternal Golden Braid
The Free Dictionary:
1. Biology Similarity in form, as in organisms of different ancestry.
2. Mathematics A one-to-one correspondence between the elements of two sets such that the result of an operation on elements of one set corresponds to the result of the analogous operation on their images in the other set.
3. A close similarity in the crystalline structure of two or more substances of similar chemical composition.