racing car vs racer

racing car and racer both are nouns.

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

As nouns, racing car and racer are synonyms defined as:

Other synonyms of racing car include race car.

racing car (noun)	racer (noun)
a fast car that competes in races	an animal that races
	slender fast-moving North American snakes
	a fast car that competes in races
	someone who drives racing cars at high speeds