xenon(n = noun.substance) atomic number 54, xe - a colorless odorless inert gaseous element occurring in the earth's atmosphere in trace amounts;
is a kind of chemical element, element, argonon, inert gas, noble gas

   A very heavy, inert gaseous element of the noble gas group, 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 -107° C., and to a solid which melts at -111.9° C. Symbol Xe (formely also X); atomic number 54; atomic weight 131.3. [Webster 1913 Suppl.]

xenon, n. Chem. a heavy colourless odourless inert gaseous element occurring in traces in the atmosphere and used in fluorescent lamps.

Usage:
Symb.: Xe.

Etymology:
Gk, neut. of xenos strange