oxycephaly vs birth defect

oxycephaly and birth defect both are nouns.

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

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

oxycephaly: a congenital abnormality of the skull; the top of the skull assumes a cone shape
birth defect: a defect that is present at birth

oxycephaly (noun)	birth defect (noun)
a congenital abnormality of the skull; the top of the skull assumes a cone shape	a defect that is present at birth