syndactyly vs birth defect

syndactyly and birth defect both are nouns.

Word	Noun	Adjective	Verb	Adverb
syndactyly	Yes	No	No	No
birth defect	Yes	No	No	No

As nouns, birth defect is a hypernym of syndactyly; that is, birth defect is a word with a broader meaning than syndactyly:

syndactyly: birth defect in which there is partial or total webbing connecting two or more fingers or toes
birth defect: a defect that is present at birth

syndactyly (noun)	birth defect (noun)
birth defect in which there is partial or total webbing connecting two or more fingers or toes	a defect that is present at birth