compact car vs auto

compact car and auto both are nouns.

Word	Noun	Adjective	Verb	Adverb
compact car	Yes	No	No	No
auto	Yes	No	No	No

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

compact car: a small and economical car
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

Other hypernyms of compact car include automobile, car, machine, motorcar.

compact car (noun)	auto (noun)
a small and economical car	a motor vehicle with four wheels; usually propelled by an internal combustion engine