frontiersman vs adult male

frontiersman and adult male both are nouns.

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

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

Other hypernyms of frontiersman include man, pioneer.

frontiersman (noun)	adult male (noun)
a man who lives on the frontier	an adult person who is male (as opposed to a woman)