n. Chem. a radioactive metallic element orig. obtained from pitchblende etc., used esp. in luminous materials and in radiotherapy.
Usage:
Symb.: Ra.
Phrases and idioms:
radium bomb a container holding a large quantity of radium and used in radiotherapy as a source of gamma rays. radium emanation RADON. radium therapy the treatment of disease by the use of radium.
Etymology: L radius ray