oarsman vs adult male

oarsman and adult male both are nouns.

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

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

Other hypernyms of oarsman include man, rower.

oarsman (noun)	adult male (noun)
a male who rows a boat	an adult person who is male (as opposed to a woman)