orca vs dolphin

orca and dolphin both are nouns.

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

As nouns, dolphin is a hypernym of orca; that is, dolphin is a word with a broader meaning than orca:

orca: predatory black-and-white toothed whale with large dorsal fin; common in cold seas
dolphin: any of various small toothed whales with a beaklike snout; larger than porpoises

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