captain vs police officer

captain and police officer both are nouns.

Word	Noun	Adjective	Verb	Adverb
captain	Yes	No	Yes	No
police officer	Yes	No	No	No

As nouns, police officer is a hypernym of captain; that is, police officer is a word with a broader meaning than captain:

Other hypernyms of captain include officer.

captain (noun)	police officer (noun)
a dining-room attendant who is in charge of the waiters and the seating of customers	a member of a police force
the pilot in charge of an airship
the naval officer in command of a military ship
an officer who is licensed to command a merchant ship
a policeman in charge of a precinct
an officer holding a rank below a major but above a lieutenant
the leader of a group of people

captain (verb)	police officer (verb)
be the captain of a sports team