SUBSTANCE [U] › a hard, natural substance that is found in the ground: a stone wall ROCK [C] › a small rock or piece of rock JEWEL [C] › a hard, valuable substance that is often used in jewellery: precious stones WEIGHT [C] (plural stone) UK › a unit for measuring weight, equal to 6.35 kilograms or 14 pounds: I gained two stone when I was pregnant. SEED [C] › the hard seed that is at the centre of some fruits: a cherry stone → See also stepping-stone