radium
Cross references: 1. element ra.di.um \'ra-d-e--*m\ n [NL, fr. L radius ray] often attrib : an intensely radioactive shining white metallic element that resembles b arium chemically, occurs in combination in minute quantities in minerals (as pitchblende or carnotite), emits alpha particles and gamma rays to form radon, and is used chiefly in luminous materials and in the treatment of cancer