officer vs policeman

officer and policeman both are nouns.

Word	Noun	Adjective	Verb	Adverb
officer	Yes	No	Yes	No
policeman	Yes	No	No	No

As nouns, policeman is a hyponym of officer; that is, policeman is a word with a more specific, narrower meaning than officer:

officer (noun)	policeman (noun)
a member of a police force	a male 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

officer (verb)	policeman (verb)
direct or command as an officer