[water chestnut] n (1854) 1: any of a genus (Trapa and esp. 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
2: a whitish crunchy vegetable used esp. in Chinese cooking that is the peeled and often sliced tuber of a sedge (Eleocharis dulcis syn. E. tuberosa) native to Asia but widely cultivated elsewhere; also: the tuber or the sedge itself