racing car vs motorcar

racing car and motorcar both are nouns.

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

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

racing car: a fast car that competes in races
motorcar: a motor vehicle with four wheels; usually propelled by an internal combustion engine

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

racing car (noun)	motorcar (noun)
a fast car that competes in races	a motor vehicle with four wheels; usually propelled by an internal combustion engine