Source : Webster's Revised Unabridged Dictionary (1913)

Addax \Ad"dax\, n. [Native name.] (Zo["o]l.)
   One of the largest African antelopes ({Hippotragus, or Oryx,
   nasomaculatus}).

   Note: It is now believed to be the {Strepsiceros} (twisted
         horn) of the ancients. By some it is thought to be the
         pygarg of the Bible.