P.O. vs enlisted officer

P.O. and enlisted officer both are nouns.

Word	Noun	Adjective	Verb	Adverb
P.O.	Yes	No	No	No
enlisted officer	Yes	No	No	No

As nouns, enlisted officer is a hypernym of P.O.; that is, enlisted officer is a word with a broader meaning than P.O.:

P.O.: a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army
enlisted officer: a military officer appointed from enlisted personnel

Other hypernyms of P.O. include noncom, noncommissioned officer.

P.O. (noun)	enlisted officer (noun)
a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army	a military officer appointed from enlisted personnel