prowl car vs motorcar

prowl car and motorcar both are nouns.

Word	Noun	Adjective	Verb	Adverb
prowl car	Yes	No	No	No
motorcar	Yes	No	No	No

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

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

Other hypernyms of prowl car include auto, automobile, car, machine.

prowl car (noun)	motorcar (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