Wordnet 3.0
NOUN (1)
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]
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]