The Collaborative International Dictionary of English v.0.48:

Water chevrotain \Wa"ter chev`ro*tain"\ (Zool.)
   A large West African chevrotain (Hyaemoschus aquaticus). It
   has a larger body and shorter legs than the other allied
   species. Called also water deerlet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

water chevrotain
    n 1: largest chevrotain; of marshy areas of west Africa [syn:
         water chevrotain, water deer, Hyemoschus aquaticus]