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The Collaborative International Dictionary of English v.0.48 (gcide)

Oxygen \Ox"y*gen\, n. [F. oxyg[`e]ne, from Gr. 'oxy`s sharp,
acid root of gi`gnesqai to be born. So called because
originally supposed to be an essential part of every acid.]
[1913 Webster]
1. (Chem.) A colorless, tasteless, odorless, gaseous element
of atomic number 8, occurring in the free state in the
atmosphere, of which it forms about 23 per cent by weight
and about 21 per cent by volume, being slightly heavier
than nitrogen. Symbol O. Atomic weight 15.9994.
[1913 Webster PJC]

Note: It occurs combined in immense quantities, forming eight
ninths by weight of water, and probably one half by
weight of the entire solid crust of the globe, being an
ingredient of silica, the silicates, sulphates,
carbonates, nitrates, etc. Oxygen combines with all
elements (except fluorine), forming oxides, bases,
oxyacid anhydrides, etc., the process in general being
called oxidation, of which combustion is only an
intense modification. At ordinary temperatures with
most substances it is moderately active, but at higher
temperatures it is one of the most violent and powerful
chemical agents known. It is indispensable in
respiration, and in general is the most universally
active and efficient element. It may be prepared in the
pure state by heating potassium chlorate.
[1913 Webster] This element (called dephlogisticated
air by Priestley) was named oxygen by Lavoisier because
he supposed it to be a constituent of all acids. This
is not so in the case of a very few acids (as
hydrochloric, hydrobromic, hydric sulphide, etc.), but
these do contain elements analogous to oxygen in
property and action. Moreover, the fact that most
elements approach the nearer to acid qualities in
proportion as they are combined with more oxygen, shows
the great accuracy and breadth of Lavoisier's
conception of its nature.
[1913 Webster]

2. Chlorine used in bleaching. [Manufacturing name]
[1913 Webster]