racer vs auto

racer and auto both are nouns.

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

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

racer: a fast car that competes in races
auto: a motor vehicle with four wheels; usually propelled by an internal combustion engine

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

racer (noun)	auto (noun)
an animal that races	a motor vehicle with four wheels; usually propelled by an internal combustion engine
slender fast-moving North American snakes
a fast car that competes in races
someone who drives racing cars at high speeds