American buffalo vs bison

American buffalo and bison both are nouns.

Word	Noun	Adjective	Verb	Adverb
American buffalo	Yes	No	No	No
bison	Yes	No	No	No

As nouns, bison is a hypernym of American buffalo; that is, bison is a word with a broader meaning than American buffalo:

American buffalo: large shaggy-haired brown bison of North American plains
bison: any of several large humped bovids having shaggy manes and large heads and short horns

American buffalo (noun)	bison (noun)
large shaggy-haired brown bison of North American plains	any of several large humped bovids having shaggy manes and large heads and short horns