dolphin vs grampus

dolphin and grampus both are nouns.

Word	Noun	Adjective	Verb	Adverb
dolphin	Yes	No	No	No
grampus	Yes	No	No	No

As nouns, grampus is a hyponym of dolphin; that is, grampus is a word with a more specific, narrower meaning than dolphin:

dolphin: any of various small toothed whales with a beaklike snout; larger than porpoises
grampus: slaty-grey blunt-nosed dolphin common in northern seas

dolphin (noun)	grampus (noun)
any of various small toothed whales with a beaklike snout; larger than porpoises	slaty-grey blunt-nosed dolphin common in northern seas
large slender food and game fish widely distributed in warm seas (especially around Hawaii)	predatory black-and-white toothed whale with large dorsal fin; common in cold seas