Source : Webster's Revised Unabridged Dictionary (1913)

Isomorphism \I`so*mor"phism\, n. [Cf. F. isomorphisme.]
   (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 hom[oe]omorphism.

Source : WordNet®

isomorphism
     n : (biology) similarity or identity of form or shape or
         structure [syn: {isomorphy}]

Source : Free On-Line Dictionary of Computing

isomorphism
     
         A {bijective} {map} between two objects which
        preserves, in both directions, any structure under
        consideration.  Thus a `group isomorphism' preserves group
        structure; an order isomorphism (between {poset}s) preserves
        the order relation, and so on.  Usually it is clear from
        context what sort of isomorphism is intended.
     
        (1995-03-25)