[ ok-si-juh n ]
/ ˈɒk sɪ dʒən /

noun Chemistry.

a colorless, odorless, gaseous element constituting about one-fifth of the volume of the atmosphere and present in a combined state in nature. It is the supporter of combustion in air and was the standard of atomic, combining, and molecular weights until 1961, when carbon 12 became the new standard. Symbol: O; atomic weight: 15.9994; atomic number: 8; density: 1.4290 g/l at 0°C and 760 mm pressure.

Nearby words

  1. oxychromatic,
  2. oxycodone,
  3. oxycodone hydrochloride,
  4. oxycontin,
  5. oxyesthesia,
  6. oxygen acid,
  7. oxygen affinity hypoxia,
  8. oxygen bar,
  9. oxygen capacity,
  10. oxygen consumption

Origin of oxygen

1780–90; < French oxygène, equivalent to oxy- oxy-1 + -gène -gen

Related formsox·y·gen·ic [ok-si-jen-ik] /ˌɒk sɪˈdʒɛn ɪk/, ox·yg·e·nous [ok-sij-uh-nuh s] /ɒkˈsɪdʒ ə nəs/, adjectiveox·y·gen·ic·i·ty [ok-si-juh-nis-i-tee] /ˌɒk sɪ dʒəˈnɪs ɪ ti/, noun

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for oxygen

British Dictionary definitions for oxygen


/ (ˈɒksɪdʒən) /


  1. a colourless odourless highly reactive gaseous element: the most abundant element in the earth's crust (49.2 per cent). It is essential for aerobic respiration and almost all combustion and is widely used in industry. Symbol: O; atomic no: 8; atomic wt: 15.9994; valency: 2; density: 1.429 kg/m³; melting pt: –218.79°C; boiling pt: –182.97°C
  2. (as modifier)an oxygen mask
Derived Formsoxygenic (ˌɒksɪˈdʒɛnɪk) or oxygenous (ɒkˈsɪdʒɪnəs), adjective

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for oxygen



gaseous chemical element, 1790, from French oxygène, coined in 1777 by French chemist Antoine-Laurent Lavoisier (1743-1794), from Greek oxys "sharp, acid" (see acrid) + French -gène "something that produces" (from Greek -genes "formation, creation;" see -gen).

Intended to mean "acidifying (principle)," it was a Greeking of French principe acidifiant. So called because oxygen was then considered essential in the formation of acids (it is now known not to be). The element was isolated by Priestley (1774), who, using the old model of chemistry, called it dephlogisticated air. The downfall of the phlogiston theory required a new name, which Lavoisier provided.

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for oxygen


[ ŏksĭ-jən ]

n. Symbol O

An element constituting 21 percent of the atmosphere by volume that occurs as a diatomic gas, O2, combines with most elements, is essential for plant and animal respiration, and is required for nearly all combustion. Atomic number 8.
A medicinal gas used therapeutically for oxygen supplementation, containing not less than 99.0 percent, by volume, of O2.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for oxygen


[ ŏksĭ-jən ]


A nonmetallic element that exists in its free form as a colorless, odorless gas and makes up about 21 percent of the Earth's atmosphere. It is the most abundant element in the Earth's crust and occurs in many compounds, including water, carbon dioxide, and iron ore. Oxygen combines with most elements, is required for combustion, and is essential for life in most organisms. Atomic number 8; atomic weight 15.9994; melting point -218.8°C; boiling point -182.9°C; gas density at 0°C 1.429 grams per liter; valence 2. See Periodic Table.

Word History

In 1786, the French chemist Antoine Lavoisier coined a term for the element oxygen (oxygène in French). He used Greek words for the coinage: oxy- means “sharp,” and -gen means “producing.” Oxygen was called the “sharp-producing” element because it was thought to be essential for making acids. Lavoisier also coined the name of the element hydrogen, the “water-producing” element, in 1788. Soon after, in 1791, another French chemist, J. A. Chaptal, introduced the word nitrogen, the “niter-producing” element, referring to its discovery from an analysis of nitric acid.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Culture definitions for oxygen


An element, normally a gas, that makes up about one-fifth of the atmosphere of the Earth. Oxygen is usually found as a molecule made up of two atoms. Its symbol is O.


When we breathe in oxygen, it is carried by the hemoglobin in our blood throughout the body, where it is used to generate energy by oxidation. (See respiration.)


Oxygen is a waste product of green plants and photosynthesis.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.