syndactyly vs syndactylism

syndactyly and syndactylism both are nouns.

Word	Noun	Adjective	Verb	Adverb
syndactyly	Yes	No	No	No
syndactylism	Yes	No	No	No

As nouns, syndactyly and syndactylism are synonyms defined as:

syndactyly and syndactylism: birth defect in which there is partial or total webbing connecting two or more fingers or toes

syndactyly (noun)	syndactylism (noun)
birth defect in which there is partial or total webbing connecting two or more fingers or toes	birth defect in which there is partial or total webbing connecting two or more fingers or toes