the.com/water chestnut

means The edible corm of an aquatic sedge plant, prized in cooking for staying crisp even after boiling, stir-frying, or canning.

from Despite the name, it's not related to the tree chestnuts you roast — it's called that simply because the corm is roughly chestnut-shaped and chestnut-colored, and it grows submerged in mud at the bottom of ponds and paddies. The plant (Eleocharis dulcis) is in the sedge family, nowhere near the walnut-and-chestnut tree lineage. A separate, unrelated plant, the water caltrop, is sometimes also called 'water chestnut' in parts of Europe and Asia, which has muddied the name's history further — so 'water chestnut' is really a folk label pinned onto at least two different plants because of a passing resemblance to a familiar nut, not a sign of any real kinship.