a colorless odorless inert gaseous element occurring in the earth's atmosphere in trace amounts
source: WordNet 3.0
A very heavy, inert gaseous element occurring in the atmosphere in the proportion of one volume is about 20 millions. It was discovered by Ramsay and Travers in 1898. It can be condensed to a liquid boiling at -109° C., and to a solid which volatilizes without melting. Symbol Xe or X; atomic weight 130.2.