a hard greyish-white metallic element that occurs with niobium in tantalite and columbite: used in electrical capacitors in most circuit boards and in alloys to increase hardness and chemical resistance, esp in surgical instruments. Symbol: Ta; atomic no: 73; atomic wt: 180.9479; valency: 2, 3, 4, or 5; relative density: 16.654; melting pt: 3020°C; boiling pt: 5458±100°C