xenon

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A colorless, odorless, highly unreactive gaseous element found in minute quantities in the atmosphere, extracted commercially from liquefied air and used in stroboscopic, bactericidal, and laser-pumping lamps. Atomic number 54; atomic weight 131.29; melting point -111.9°C; boiling point -107.1°C; density (gas) 5.887 grams per liter; specific gravity (liquid) 3.52 (-109°C). See Table at element.

Century Dictionary and Cyclopedia

1. n. In chem., the heaviest of the five recently discovered elementary substances present in gaseous form in the atmosphere. It was first obtained by Sir William Ramsay, assisted by M. W. Travers, in 1898, as a result of the careful fractional distillation of liquid air. It is a colorless gas, of density about 65.35 (oxygen = 16), condensable to a colorless liquid of density 3.52 at its boiling-point (water = 1), which boils under normal pressure at —109.1° C. Xenon is incapable, as far as known, of chemically combining with anything else. It gives in a suitably exhausted tube by electrical discharge a characteristic spectrum, which is modified on introduction of a Leyden jar and spark-gap. Ramsay found in atmospheric air about 1 volume in 170,000,000 of air.

Wiktionary

1. n. A heavy, gaseous chemical element (symbol Xe) of the noble gases group with an atomic number of 54.

GNU Webster's 1913

1. n. (Chem.) 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.

WordNet 3.0

1. n. a colorless odorless inert gaseous element occurring in the earth's atmosphere in trace amounts