Found 2 items, similar to actinium.
English → English (WordNet) Definition: actinium actinium n : a radioactive element of the actinide series; found in uranium ores [syn: Ac, atomic number 89]
English → English (gcide) Definition: Actinium Actinium \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. [1913 Webster]