The Collaborative International Dictionary of English v.0.48:

Urus \U"rus\, n. [L.; of Teutonic origin. See Aurochs.]
   (Zool.)
   A very large, powerful, and savage extinct bovine animal
   (Bos urus or Bos primigenius) anciently abundant in
   Europe. It appears to have still existed in the time of
   Julius Caesar. It had very large horns, and was hardly
   capable of domestication. Called also, ur, ure, and
   tur.
   [1913 Webster]

WordNet (r) 3.0 (2006):

urus
    n 1: large recently extinct long-horned European wild ox;
         considered one of the ancestors of domestic cattle [syn:
         aurochs, urus, Bos primigenius]