sassaby

from WordNet (r) 3.0 (2006)

sassaby
    n 1: a large South African antelope; considered the swiftest
         hoofed mammal [syn: {sassaby}, {topi}, {Damaliscus
         lunatus}]

from The Collaborative International Dictionary of English v.0.48

Sassaby \Sas"sa*by\, Sassabye \Sas"sa*bye\, n. (Zool.)
   A large African antelope ({Alcelaphus lunata}), similar to
   the hartbeest, but having its horns regularly curved.
   [1913 Webster]