Dictionary
ac•tin•i•um
Pronunciation: (ak-tin'ē-um), [key]—
n. Chem.
a radioactive silver-white metallic element that glows blue in the dark, resembling the rare earths in chemical behavior and valence.
Symbol: Ac;
at. no.: 89;
at. wt.: 227.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.