Definition of argon

1) An element that is a member of the 8A group (Noble Gases) of the periodic table. Argon is represented by the atomic symbol Ar, has an atomic number of 18, and an atomic weight of 39.948. It is colorless, odorless, and a very inert gas. It comprises about 1% of the Earth's atmosphere.

source: [Chemical & Engineering News; v73n36; 8; 1995.] [Chemistry The Central Science; Brown, Theodore; Lemay, H. Eugene; Bursten, Bruce; p. 846; 1994; Prentice Hall; Englewood Cliffs, New Jersey.]