police car vs automobile

police car and automobile both are nouns.

Word	Noun	Adjective	Verb	Adverb
police car	Yes	No	No	No
automobile	Yes	No	Yes	No

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

police car: a car in which policemen cruise the streets; equipped with radiotelephonic communications to headquarters
automobile: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of police car include auto, car, machine, motorcar.

police car (noun)	automobile (noun)
a car in which policemen cruise the streets; equipped with radiotelephonic communications to headquarters	a motor vehicle with four wheels; usually propelled by an internal combustion engine

police car (verb)	automobile (verb)
	travel in an automobile