1766, misapplication to the European bison (Bos bison) of a word that actually refers to a species of wild ox (Bos ursus) that went extinct 17c., from German Aurochs, from Old High German urohso, from uro "aurochs" (cognate with Old English ur, Old Norse ürr), which is of unknown origin, + ohso "ox" (see ox). Latin urus and Greek ouros are Germanic loan-words.