Definition of radium in US English:



  • 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.

    • ‘Radon is present in the atmosphere because it is constantly being formed during the radioactive decay of uranium and radium.’
    • ‘The ability of radioactive substances such as radium to radiate energy, apparently spontaneously and continuously, appeared to contradict the law of the conservation of energy.’
    • ‘Rutherford was studying the structure of matter by bombarding a very thin gold foil with the alpha radiation from radium and polonium.’
    • ‘Initial autopsies showed high amounts of radium and cesium in four deer livers.’
    • ‘All isotopes of radium are radioactive with radium - 226 being the most stable.’


Late 19th century: from Latin radius ‘ray’ + -ium.