racer vs racing car

racer and racing car both are nouns.

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

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

Other synonyms of racer include race car.

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