Thorium \Tho"ri*um\, 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.

Source: Webster's Revised Unabridged Dictionary (1913)