English▸ noun the chemical element of atomic number 88, a rare radioactive metal of the alkaline earth series. It was formerly used as a source of radiation for radiotherapy. (Symbol: Ra)
Radium is the most reactive member of the alkaline earth metals. It is rare in nature, occurring chiefly as an impurity in uranium ores. Radium was formerly used extensively in the treatment of tumours and in luminous materials, but it has now been largely replaced by other substances for these purposes.