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

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

Scientists are working to improve methods for reconstructing carbon dioxide levels, studying other gases trapped in the ice, and better understanding how very old ice is preserved.

From Science Daily • Apr. 24, 2026

Speaking to Sky News on Thursday, Business Secretary Peter Kyle said the availability of carbon dioxide was not a concern for the British economy "at this moment."

From BBC • Apr. 16, 2026

The EPA estimated the 2022 emissions from flooded lands as equivalent to 44.4 million metric tons of carbon dioxide — comparable to U.S. steel and iron plants.

From Los Angeles Times • Apr. 15, 2026

The hydrogen, carbon dioxide, and methane in my gut churned.

From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas