posseman vs adult male

posseman and adult male both are nouns.

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

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

Other hypernyms of posseman include man.

posseman (noun)	adult male (noun)
an able-bodied man serving as a member of a posse	an adult person who is male (as opposed to a woman)