adult male vs grownup

adult male and grownup both are nouns.

Word	Noun	Adjective	Verb	Adverb
adult male	Yes	No	No	No
grownup	Yes	Yes	No	No

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

Other hypernyms of adult male include adult, male, male person.

adult male (noun)	grownup (noun)
an adult person who is male (as opposed to a woman)	a fully developed person from maturity onward

adult male (adjective)	grownup (adjective)
	(of animals) fully developed