Source : Webster's Revised Unabridged Dictionary (1913)

Xenon \Xen"on\, n. [Gr. ?, neut. of ? strange.] (Chem.)
   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[deg] C., and to
   a solid which volatilizes without melting. Symbol Xe or X;
   atomic weight 130.2.

Source : WordNet®

xenon
     n : a colorless odorless inert gaseous element occurring in the
         earth's atmosphere in trace amounts [syn: {Xe}, {atomic
         number 54}]