carbon dioxide

noun

: a heavy colorless gas CO2 that does not support combustion, dissolves in water to form carbonic acid, is formed especially in animal respiration and in the decay or combustion of animal and vegetable matter, is absorbed from the air by plants in photosynthesis, and is used in the carbonation of beverages

Examples of carbon dioxide in a Sentence

Recent Examples on the Web
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But the study also found that those impacts could be reduced enormously — reducing carbon dioxide emissions by 73% and water usage 86% — with smarter siting and planning of the facilities. James Rainey, Los Angeles Times, 29 Jan. 2026 The network will supply the equivalent of several thousand homes and prevent the emissions of thousands of tons of carbon dioxide (CO2). Georgina Jedikovska, Interesting Engineering, 29 Jan. 2026 Senate Bill 7 would require a carbon storage operator to receive approval from a county legislative body or plan commission if the sequestration project would transport or store carbon dioxide outside the county where it’s generated. Alexandra Kukulka, Chicago Tribune, 29 Jan. 2026 Photosynthesis involves green plants using sunlight to make nutrients from carbon dioxide and water. Gemma Johnstone, The Spruce, 29 Jan. 2026 See All Example Sentences for carbon dioxide

Word History

First Known Use

1867, in the meaning defined above

Time Traveler
The first known use of carbon dioxide was in 1867

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Cite this Entry

“Carbon dioxide.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/carbon%20dioxide. Accessed 2 Feb. 2026.

Kids Definition

carbon dioxide

noun
: a heavy colorless gas CO2 that is formed especially by the burning and breaking down of organic substances (as in animal respiration), is absorbed from the air by plants in photosynthesis, and has many industrial uses

Medical Definition

carbon dioxide

noun
: a heavy colorless gas CO2 that does not support combustion, dissolves in water to form carbonic acid, is formed especially in animal respiration and in the decay or combustion of animal and vegetable matter, is absorbed from the air by plants in photosynthesis, and is used in the carbonation of beverages

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