Webster’s Revised Unabridged Dictionary · 1913
Thorium
Tho′ri·um (thō′rĭ·ŭm), n. [NL. See Thorite.] (Chem.) A metallic element found in certain rare minerals, as thorite, pyrochlore, monazite, etc., and isolated as an infusible gray metallic powder which burns in the air and forms thoria; — formerly called also thorinum. Symbol Th. Atomic weight 232.0.