- thorium, Th, atomic number 90 - 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
--1 is a kind of metallic element, metal
--1 is a substance of monazite; thorite
--1 has particulars: thorium-228, radiothoriumDerived form: verb thoriate1