traffic cop vs police officer

traffic cop and police officer both are nouns.

Word	Noun	Adjective	Verb	Adverb
traffic cop	Yes	No	No	No
police officer	Yes	No	No	No

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

Other hypernyms of traffic cop include officer.

traffic cop (noun)	police officer (noun)
a policeman who controls the flow of automobile traffic	a member of a police force