DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   atomic number 90
       n 1: 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 [syn:
            thorium, Th, atomic number 90]