radium Syllabification: (ra·di·um)Pronunciation: /ˈrādēəm/Definition of radium 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)Origin: late 19th century: from Latin radius 'ray' + -iumradium in other Oxford dictionaries Definition of radium in the British & World English dictionary
