DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   atomic number 86
       n 1: a radioactive gaseous element formed by the disintegration
            of radium; the heaviest of the inert gasses; occurs
            naturally (especially in areas over granite) and is
            considered a hazard to health [syn: radon, Rn, atomic
    number 86]