oxygen

American  

[ok-si-juhn] / ˈɒk sɪ dʒən /

noun

Chemistry.

1. 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. O; 15.9994; 8; density: 1.4290 grams/liter at 0°C and 760 millimeter pressure.

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oxygen British  

/ ɒkˈsɪdʒɪnəs, ˌɒksɪˈdʒɛnɪk, ˈɒksɪdʒən /

noun

1. 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

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oxygen Scientific  

/ ŏk′sĭ-jən /

1. 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.

2. See Periodic Table

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oxygen Cultural  

1. 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.

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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.

Discover More

Oxygen is a waste product of green plants and photosynthesis.

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.)

Other Word Forms

• oxygenic adjective
• oxygenicity noun
• oxygenous adjective

Etymology

Origin of oxygen

First recorded in 1780–90; from French oxygène, equivalent to oxy- + -gène; see origin at oxy- ¹, -gen

Explanation

Oxygen is air, the stuff we breathe, the thing that makes our lives possible. It is an element, a basic chemical found on the earth. In fact, we don't breathe pure oxygen; our air is about 20 percent oxygen. Still, oxygen is everywhere—it’s the third most common element on earth. Usually, the word is used in scientific contexts. Still, when someone has a big personality and likes to be the center of attention, we say, they "take all the oxygen out of the room." That means they are a blowhard and attention hog. If they really took your oxygen, you’d be dead.

Example Sentences

The top of the device remains exposed to air, ensuring a steady oxygen supply.

From Science Daily • Apr. 19, 2026

He developed a cold as a baby which deteriorated so much that he was taken to hospital, diagnosed with RSV and put on oxygen.

From BBC • Apr. 17, 2026

In this A.I.-powered asphyxiation of the information ecosystem, Spero has positioned himself on social media as a folk hero hauling in the oxygen tanks.

From Slate • Apr. 17, 2026

He simply hoped to find the strength to descend to an altitude with softer beds, more oxygen and higher temperatures.

From The Wall Street Journal • Apr. 15, 2026

How long before I breathe up all the oxygen?

From "Muffled" by Jennifer Gennari