Source : Webster's Revised Unabridged Dictionary (1913)

Water chestnut \Wa"ter chest"nut\ (Bot.)
   The fruit of {Trapa natans} and {Trapa bicornis}, Old World
   water plants bearing edible nutlike fruits armed with several
   hard and sharp points; also, the plant itself; -- called also
   {water caltrop}.

Saligot \Sal"i*got\, n. [F.] (Bot.)
   The water chestnut ({Trapa natans}).

Source : WordNet®

Trapa natans
     n : a variety of water chestnut [syn: {water caltrop}, {Jesuits'
         nut}]