brachycephalic vs adult

brachycephalic and adult both are nouns.

Word	Noun	Adjective	Verb	Adverb
brachycephalic	Yes	Yes	No	No
adult	Yes	Yes	No	No

As nouns, adult is a hypernym of brachycephalic; that is, adult is a word with a broader meaning than brachycephalic:

Other hypernyms of brachycephalic include grownup.

brachycephalic (noun)	adult (noun)
an adult with a short broad head	any mature animal
	a fully developed person from maturity onward

brachycephalic (adjective)	adult (adjective)
having a short broad head with a cephalic index of over 80	(of animals) fully developed
	designed to arouse lust