used-car vs motorcar

used-car and motorcar both are nouns.

Word	Noun	Adjective	Verb	Adverb
used-car	Yes	No	No	No
motorcar	Yes	No	No	No

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

used-car: a car that has been previously owned; not a new car
motorcar: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of used-car include auto, automobile, car, machine.

used-car (noun)	motorcar (noun)
a car that has been previously owned; not a new car	a motor vehicle with four wheels; usually propelled by an internal combustion engine