automobile vs auto

automobile and auto both are nouns.

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

As nouns, automobile and auto are synonyms defined as:

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

Other synonyms of automobile include car, machine, motorcar.

automobile (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

automobile (verb)	auto (verb)
travel in an automobile