black bear vs Ursus americanus

black bear and Ursus americanus both are nouns.

Word	Noun	Adjective	Verb	Adverb
black bear	Yes	No	No	No
Ursus americanus	Yes	No	No	No

As nouns, black bear and Ursus americanus are synonyms defined as:

black bear and Ursus americanus: brown to black North American bear; smaller and less ferocious than the brown bear

Other synonyms of black bear include American black bear, Euarctos americanus.

black bear (noun)	Ursus americanus (noun)
brown to black North American bear; smaller and less ferocious than the brown bear	brown to black North American bear; smaller and less ferocious than the brown bear
bear with a black coat living in central and eastern Asia