actinium Meaning, Definition & Usage

  1. noun a radioactive element of the actinide series; found in uranium ores
    atomic number 89; Ac.

WordNet

Ac*tin"i*um noun
Etymology
Gr. , , ray.
Definitions
  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.

Webster 1913