buffalo vs bison

buffalo and bison both are nouns.

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

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

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

buffalo (noun)	bison (noun)
any of several Old World animals resembling oxen including, e.g., water buffalo, Cape buffalo	any of several large humped bovids having shaggy manes and large heads and short horns
large shaggy-haired brown bison of North American plains
meat from an American bison

buffalo (verb)	bison (verb)
intimidate or overawe