The Collaborative International Dictionary of English v.0.48:

Gemsbok \Gems"bok\, n. [D.; akin to G. gemsbock the male or buck
   of the chamois; gemse chamois, goat of the Alps + bock buck.]
   (Zool.)
   A South African antelope (Oryx Capensis), having long,
   sharp, nearly straight horns.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gemsbok
    n 1: large South African oryx with a broad black band along its
         flanks [syn: gemsbok, gemsbuck, Oryx gazella]