water chestnut Definition

any of a genus (Trapa, especially T. natans of the family Trapaceae, the water-chestnut family) of Old World aquatic herbs sometimes grown as ornamentals; also : its edible nutlike spiny fruit

a whitish crunchy vegetable used especially in Chinese cooking that is the peeled and often sliced tuber of a sedge (Eleocharis dulcis synonym E. tuberosa) native to Asia but widely cultivated elsewhere; also : the tuber or the sedge itself