subcompact car vs auto

subcompact car and auto both are nouns.

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

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

subcompact car: a car smaller than a compact car
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

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

subcompact car (noun)	auto (noun)
a car smaller than a compact car	a motor vehicle with four wheels; usually propelled by an internal combustion engine