stock car vs racer

stock car and racer both are nouns.

Word	Noun	Adjective	Verb	Adverb
stock car	Yes	No	No	No
racer	Yes	No	No	No

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

stock car: a racing car with the basic chassis of a commercially available car
racer: a fast car that competes in races

Other hypernyms of stock car include race car, racing car.

stock car (noun)	racer (noun)
a racing car with the basic chassis of a commercially available car	an animal that races
a car kept in dealers' stock for regular sales	slender fast-moving North American snakes
	a fast car that competes in races
	someone who drives racing cars at high speeds