greyhound vs racer

greyhound and racer both are nouns.

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

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

greyhound: a tall slender dog of an ancient breed noted for swiftness and keen sight; used as a racing dog
racer: an animal that races

Other hypernyms of greyhound include hound, hound dog.

greyhound (noun)	racer (noun)
a tall slender dog of an ancient breed noted for swiftness and keen sight; used as a racing dog	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