grizzly bear vs brown bear

grizzly bear and brown bear both are nouns.

Word	Noun	Adjective	Verb	Adverb
grizzly bear	Yes	No	No	No
brown bear	Yes	No	No	No

As nouns, brown bear is a hypernym of grizzly bear; that is, brown bear is a word with a broader meaning than grizzly bear:

grizzly bear: powerful brownish-yellow bear of the uplands of western North America
brown bear: large ferocious bear of Eurasia

Other hypernyms of grizzly bear include bruin, Ursus arctos.

grizzly bear (noun)	brown bear (noun)
powerful brownish-yellow bear of the uplands of western North America	large ferocious bear of Eurasia