motorcar vs auto

motorcar and auto both are nouns.

Word	Noun	Adjective	Verb	Adverb
motorcar	Yes	No	No	No
auto	Yes	No	No	No

As nouns, motorcar and auto are synonyms defined as:

motorcar and auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other synonyms of motorcar include automobile, car, machine.

motorcar (noun)	auto (noun)
a motor vehicle with four wheels; usually propelled by an internal combustion engine	a motor vehicle with four wheels; usually propelled by an internal combustion engine