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.

---

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

---

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

---

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.

---

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; oxy- ¹, -gen

Example Sentences

An oxygen tank had exploded in their spacecraft, forcing them to abort their lunar landing plans.

From Barron's • Apr. 4, 2026

Several explosions from exploding oxygen canisters within the ambulances caused windows of nearby buildings, including the synagogue to crack or shatter - however no injuries were reported.

From BBC • Apr. 1, 2026

But in Jane’s heart, it did mix, so her tiny body received less oxygen than it required.

From Slate • Mar. 29, 2026

By mapping how oxygen levels vary across NGC 1365 and comparing those observations with advanced simulations from the Illustris Project, the team reconstructed how the galaxy developed over 12 billion years.

From Science Daily • Mar. 23, 2026

“What is life like on your cat planet? Is there oxygen there? Trees? Mice? Houses?”

From "Klawde: Evil Alien Warlord Cat" by Johnny Marciano and Emily Chenoweth