beluga vs dolphin

beluga and dolphin both are nouns.

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

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

beluga: small northern whale that is white when adult
dolphin: any of various small toothed whales with a beaklike snout; larger than porpoises

beluga (noun)	dolphin (noun)
valuable source of caviar and isinglass; found in Black and Caspian seas	any of various small toothed whales with a beaklike snout; larger than porpoises
small northern whale that is white when adult	large slender food and game fish widely distributed in warm seas (especially around Hawaii)