black racer vs racer

black racer and racer both are nouns.

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

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

black racer: blackish racer of the eastern United States that grows to six feet
racer: slender fast-moving North American snakes

black racer (noun)	racer (noun)
blackish racer of the eastern United States that grows to six feet	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