police chief vs officer

police chief and officer both are nouns.

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

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

Other hypernyms of police chief include police officer.

police chief (noun)	officer (noun)
a policeman in charge of a precinct	a member of a police force
	someone who is appointed or elected to an office and who holds a position of trust
	any person in the armed services who holds a position of authority or command
	a person authorized to serve in a position of authority on a vessel

police chief (verb)	officer (verb)
	direct or command as an officer