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