The Collaborative International Dictionary of English v.0.48:
Addax \Ad"dax\, n. [Native name.] (Zool.) One of the largest African antelopes (Hippotragusnasomaculatus or Oryx nasomaculatus). [1913 Webster] 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. [1913 Webster]