An aurochs is a large horned creature, also known as a "Taurus", which is described in the ancient "Booke" which has been memorized by the village eldress in Lower Posada.

The horned aurochs or Taurus, she recited, erroneously called bison by some ignoramuses. It hath horns and useth them to ram—.

— page 179, The Last Wish (UK edition)