Definition of water chestnut
noun
1 (also Chinese water chestnut) the crisp, white-fleshed tuber of a tropical sedge, used in oriental cookery.
2the sedge which yields the water chestnut, which is cultivated in flooded fields in SE Asia. - Eleocharis tuberosa, family Cyperaceae
3 (also water caltrop) an aquatic plant with small white flowers, producing an edible rounded seed with two large projecting horns. - Trapa natans, family Trapaceae