sameness vs similarity

sameness and similarity both are nouns.

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

As nouns, similarity is a hyponym of sameness; that is, similarity is a word with a more specific, narrower meaning than sameness:

Other hyponyms of sameness include identicalness, identity, indistinguishability, equality.

sameness (noun)	similarity (noun)
the quality of being alike	the quality of being similar
the quality of wearisome constancy, routine, and lack of variety	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