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

Unlike gas-fired power generation, which emits carbon dioxide emissions, geothermal heat is carbon-free.

From The Wall Street Journal • May 13, 2026

Methane, the second biggest contributor to climate change, stays in the atmosphere for far less time than carbon dioxide, but its warming effect is roughly 80 times more potent over a 20-year period.

From Barron's • May 4, 2026

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

From BBC • Apr. 29, 2026

The Clean Power Plan would have required states and energy companies to shift electricity production from higher-emitting to lower-emitting production methods to reduce carbon dioxide emissions.

From Salon • Apr. 25, 2026

A single CFC molecule is about ten thousand times more efficient at exacerbating greenhouse effects than a molecule of carbon dioxide–and carbon dioxide is of course no slouch itself as a greenhouse gas.

From "A Short History of Nearly Everything" by Bill Bryson