bison vs aurochs

bison and aurochs both are nouns.

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

As nouns, aurochs is a hyponym of bison; that is, aurochs 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
aurochs: European bison having a smaller and higher head than the North American bison

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

bison (noun)	aurochs (noun)
any of several large humped bovids having shaggy manes and large heads and short horns	large recently extinct long-horned European wild ox; considered one of the ancestors of domestic cattle
	European bison having a smaller and higher head than the North American bison