THORIUM

thorium, Th, atomic number

(noun) a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands

Source: WordNet® 3.1

Etymology

Noun

thorium (uncountable)

A chemical element (symbol Th) with atomic number 90: a weakly radioactive, malleable, moderately hard silvery metal that tarnishes black when exposed to air.

Synonyms

• thorinum (former alternative form; obsolete)

Source: Wiktionary

Tho"ri*um, n. Etym: [NL. See Thorite.] (Chem.)

Definition: 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 Unabridged Dictionary 1913 Edition