police chief vs police captain

police chief and police captain both are nouns.

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

As nouns, police chief and police captain are synonyms defined as:

Other synonyms of police chief include captain.

police chief (noun)	police captain (noun)
a policeman in charge of a precinct	a policeman in charge of a precinct