syndactyly vs congenital defect

syndactyly and congenital defect both are nouns.

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

As nouns, congenital defect is a hypernym of syndactyly; that is, congenital 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
congenital defect: a defect that is present at birth

Other hypernyms of syndactyly include birth defect, congenital abnormality, congenital anomaly, congenital disorder.

syndactyly (noun)	congenital 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