carbon dioxide

American  

[kahr-buhn dahy-ok-sahyd] / ˈkɑr bən daɪˈɒk saɪd /

noun

1. a colorless, odorless, incombustible gas, CO 2 , present in the atmosphere and formed during respiration, usually obtained from coal, coke, or natural gas by combustion, from carbohydrates by fermentation, by reaction of acid with limestone or other carbonates, or naturally from springs: used extensively in industry as dry ice, or carbon dioxide snow, in carbonated beverages, fire extinguishers, etc.

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carbon dioxide British  

noun

1. Also called: carbonic-acid gas.  a colourless odourless incombustible gas present in the atmosphere and formed during respiration, the decomposition and combustion of organic compounds, and in the reaction of acids with carbonates: used in carbonated drinks, fire extinguishers, and as dry ice for refrigeration. Formula: CO 2

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carbon dioxide Scientific  

1. A colorless, odorless gas that is present in the atmosphere and is formed when any fuel containing carbon is burned. It is breathed out of an animal's lungs during respiration, is produced by the decay of organic matter, and is used by plants in photosynthesis. Carbon dioxide is also used in refrigeration, fire extinguishers, and carbonated drinks. Chemical formula: CO ₂ .

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carbon dioxide Cultural  

1. A compound made up of molecules containing one carbon atom and two oxygen atoms.

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Discover More

Carbon dioxide is normally found as a gas that is breathed out by animals and absorbed by green plants. The plants, in turn, return oxygen to the atmosphere. (See carbon cycle and respiration.)

Carbon dioxide is also given off in the burning of fossil fuels (see greenhouse effect).

Etymology

Origin of carbon dioxide

First recorded in 1870–75

Compare meaning

How does carbon-dioxide compare to similar and commonly confused words? Explore the most common comparisons:

• carbon monoxide vs. carbon dioxide

Example Sentences

See Examples For:

carbon dioxide

Candidatus Velamenicoccus archaeovorus feeds on microorganisms that convert limonene, the compound responsible for the scent of oranges, into methane and carbon dioxide.

From Science Daily ● Aug. 5, 2026

And, similarly, in multiple proceedings, it ignored the benefits of reducing the emissions of greenhouse gases, including carbon dioxide, methane, and hydrofluorocarbons.

From Slate ● Aug. 2, 2026

Alternatively, the acidic water can flow out to the ocean where its reaction with seawater likewise releases carbon dioxide.

From Barron's ● Jul. 22, 2026

Tropical rainforests like the Amazon are home to millions of species, and in a healthy state they absorb vast quantities of planet-warming carbon dioxide, helping to keep the Earth cool.

From BBC ● Jul. 21, 2026

All of the carbon in our bodies was originally floating in the air, as part of a carbon dioxide molecule.

From "The Omnivore's Dilemma" by Michael Pollan