[1] : The Collaborative International Dictionary of English v.0.48

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.
   1913 webster
see also:
trapa natans trapa bicornis water caltrop 

[2] : WordNet (r) 2.0

trapa bicornis
     n : water chestnut whose spiny fruit has two rather than 4
         prongs syn: ling, ling ko
see also:
ling ling ko 

Trapa >> T Words
Trapa, definition of term: Trapa
trapa_pag1.html