Actinium

n.

1.

(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.

Noun

1.

actinium - a radioactive element of the actinide series; found in uranium ores Synonyms: Ac, atomic number 89

Ac, atomic number 89, chemical element, element, uranium ore