Water chestnut : 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.

Example:


Taxonomy
water chestnut, Eleocharis dulcis, unranked, vegetables, free encyclopedia, The Chinese, Chinese water chestnut, corms, Taste, Water caltrop, unrelated, thầy, năng, crisp, dry weight, caltrops, genus Trapa, search.

Defination from the web:
water chestnut cake, which is common as part of dim sum cuisine. ... Boiled water chestnut has a firm, and slightly crunchy texture. The flavor is very mild, slightly nutty in taste, though is easily overpowered by any ...