Definition of: oxygen

(ok′sə·jin) noun
A colorless, tasteless, odorless gaseous element (symbol O, atomic number 8), occurring free in the atmosphere and combined in numerous compounds (of which water is the most familiar), comprising 21 percent by volume of the atmosphere and about 49 percent by weight of the lithosphere, the agent in combustion and an element essential to the formation and functioning of all forms of life. See PERIODIC TABLE. [<F oxygène <oxy- OXY-¹ + -gène -GEN; so called because formerly considered essential to all acids]