Main Entry:

ra·dio·ac·tiv·i·ty

Pronunciation:

\-ak-ˈti-və-tē\

Function:

noun

Etymology:

International Scientific Vocabulary

Date:

1899

: the property possessed by some elements (as uranium) or isotopes (as carbon 14) of spontaneously emitting energetic particles (as electrons or alpha particles) by the disintegration of their atomic nuclei ; also : the rays emitted