The Collaborative International Dictionary of English v.0.48:

Pygarg \Py"garg\, Pygargus \Py*gar"gus\, [L. pygargus, Gr. ?,
   literally, white rump; ? the rump + white: cf. F. pygargue.]
   1. (Zool.) A quadruped, probably the addax, an antelope
      having a white rump. --Deut. xiv. 5.
      [1913 Webster]

   2. (Zool.)
      (a) The female of the hen harrier.
      (b) The sea eagle.
          [1913 Webster]