isomorphism vs similarity

isomorphism and similarity both are nouns.

Word	Noun	Adjective	Verb	Adverb
isomorphism	Yes	No	No	No
similarity	Yes	No	No	No

As nouns, similarity is a hypernym of isomorphism; that is, similarity is a word with a broader meaning than isomorphism:

isomorphism (noun)	similarity (noun)
(biology) similarity or identity of form or shape or structure	the quality of being similar
	a Gestalt principle of organization holding that (other things being equal) parts of a stimulus field that are similar to each other tend to be perceived as belonging together as a unit