isomorphism

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Biology Similarity in form, as in organisms of different ancestry.
2. n. 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. n. A close similarity in the crystalline structure of two or more substances of similar chemical composition.

Century Dictionary and Cyclopedia

1. n. A similarity of crystalline form: as, between substances of analogous composition or atomic proportions, as the members of a group of compounds like the sulphates of barium, strontium, and lead
2. n. between compounds of unlike composition or atomic proportions. The first of these is isomorphism proper, and is sometimes distinguished as isomerous or isonomic isomorphism; the second as heteromerous or heteronomic isomorphism, or simply as homæomorphism.
3. n. In biology, the state or condition of being different in ancestry, but alike in appearance. See isomorphic, 2 .
4. n. In group-theory, the state or character of being isomorphic.

Wiktionary

1. n. Similarity of form

GNU Webster's 1913

1. n. (Crystallog.) A similarity of crystalline form between substances of similar composition, as between the sulphates of barium (BaSO4) and strontium (SrSO4). It is sometimes extended to include similarity of form between substances of unlike composition, which is more properly called homœomorphism.
2. n. (Math.) A one-to-one mapping of one set onto another set which preserves the relations between the elements of the domains of the sets.

WordNet 3.0

1. n. (biology) similarity or identity of form or shape or structure