radium
n. uncountablen. a radioactive metal that was once used to make things glow in the dark. It is very dangerous because it can hurt your body if you are exposed to it for too long.
n. a radioactive alkaline-earth metal with the atomic number 88. Historically used in luminous paints and medical treatments, it is now primarily of interest in nuclear physics and as a source of alpha particles.
The old clock hands were painted with radium to glow at night.
Scientists in the early twentieth century discovered that radium could be used to treat certain types of cancer, though its dangers were not yet understood.
The discovery of radium by the Curies revolutionized the field of radiochemistry, though the subsequent health risks associated with its handling eventually led to its replacement by safer isotopes.
Borrowed from French radium, from rad(ioactif) (“radioactive”) + -ium (suffix used to form the names of metallic elements).