water chestnut

from WordNet (r) 3.0 (2006)

water chestnut
    n 1: a plant of the genus Trapa bearing spiny four-pronged
         edible nutlike fruits [syn: {water chestnut}, {water
         chestnut plant}, {caltrop}]
    2: Chinese sedge yielding edible bulb-shaped tubers [syn: {water
       chestnut}, {Chinese water chestnut}, {Eleocharis dulcis}]
    3: edible bulbous tuber of a Chinese marsh plant

from 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]

[email protected]