Water caltrop (Trapa bicornis and Trapa natans), often called by its Hindi name, singhara, is an aquatic plant bearing a single edible seed. It is often referred to as a "water chestnut" but it is unrelated to the Chinese water chestnut (Eleocharis dulcis).
The distinctive lozenge shape of the nut has given rise to two synonyms: Japanese "hishi" is both the name of the nut and a diamond, lozenge, or rhombus shape; and in Eastern India and Bangladesh, the Sanskrit name Shringataka was shortened to Bengal "shingara", which refers to the distinctive diamond-shaped samosas prepared in that region.