car vs auto

car and auto both are nouns.

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

As nouns, car and auto are synonyms defined as:

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

Other synonyms of car include automobile, machine, motorcar.

car (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
a wheeled vehicle adapted to the rails of railroad
where passengers ride up and down
the compartment that is suspended from an airship and that carries personnel and the cargo and the power plant
a conveyance for passengers or freight on a cable railway