ox·y·gen 
(ŏksĭ-jən)
(ŏksĭ-jən)n. Symbol O
A nonmetallic element constituting 21 percent of the atmosphere by volume that occurs as a diatomic gas, O2, and in many compounds such as water and silica, and in iron ore. It combines with most elements, is essential for plant and animal respiration, and is required for nearly all combustion. Ozone, O3, is an allotrope of this element. Atomic number 8; atomic weight 15.9994; melting point -218.79°C; boiling point -182.9°C; gas density at 0°C 1.429 grams per liter; valence 2. See Periodic Table.
[French oxygène : Greek oxus, sharp, acid; see ak- in the Appendix of Indo-European roots + French -gène, -gen.]
ox′y·genic (-jĕnĭk) adj.
ox′y·geni·cal·ly adv.
ox·yge·nous (ŏk-sĭjə-nəs) adj.
Word History: One of the most important substances on earth is misnamed. The word oxygen is the Anglicized form of French oxygène, the name for the element proposed in a work entitled Méthode de nomenclature chimique (1787) by a collaborative of chemists including Antoine Laurent Lavoisier, Louis Bernard de Guyton de Morveau, Claude Louis Berthollet, and Antoine François de Fourcroy. (Oxygen had been discovered a few years before by Joseph Priestley in 1774, and he had called the gas dephlogisticated air.) The same publication also introduced the French words that were soon adopted into English as hydrogen and sodium chloride (common salt), among other terms commonly used in chemistry. The French word oxygène was intended to mean "acid-producing," from the Greek word oxus, "sharp," used in the sense "acid," and the Greek suffix -genes, "born," misinterpreted as "producing." At the time oxygen was thought to be an essential component of an acid. Although this is not the case, the name oxygen has persisted for the element.