1766, misapplication to the European bison (Bos bison) of a word that actually refers to a species of wild cattle (Bos ursus) that went extinct early 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.
