Definitions for: Actinium

[n] a radioactive element of the actinide series; found in uranium ores

Webster (1913) Definition: Ac*tin"i*um, n. [Gr. ?, ?, ray.] (Chem.)
A supposed metal, said by Phipson to be contained in
commercial zinc; -- so called because certain of its
compounds are darkened by exposure to light.

Synonyms: Ac, atomic number 89

See Also: chemical element, element, uranium ore