Main Entry:

ra·di·um

Pronunciation:

\ˈrā-dē-əm\

Function:

noun

Usage:

often attributive

Etymology:

New Latin, from Latin radius ray

Date:

1899

: an intensely radioactive brilliant white metallic element that resembles barium chemically, occurs in combination in minute quantities in minerals (as pitchblende or carnotite), emits alpha particles and gamma rays to form radon, and is used chiefly in luminous materials and in the treatment of cancer — see element table