bison vs Bison bison

bison and Bison bison both are nouns.

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

As nouns, Bison bison is a hyponym of bison; that is, Bison bison is a word with a more specific, narrower meaning than bison:

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

Other hyponyms of bison include American bison, American buffalo, buffalo, aurochs, Bison bonasus, wisent.

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