carbon monoxide

American  

noun

1. a colorless, odorless, poisonous gas, CO, that burns with a pale-blue flame, produced when carbon burns with insufficient air: used chiefly in organic synthesis, metallurgy, and in the preparation of metal carbonyls, as nickel carbonyl.

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carbon monoxide British  

noun

1. a colourless odourless poisonous flammable gas formed when carbon compounds burn in insufficient air and produced by the action of steam on hot carbon: used as a reducing agent in metallurgy and as a fuel. Formula: CO

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Etymology

Origin of carbon monoxide

First recorded in 1870–75

Compare meaning

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

• carbon monoxide vs. carbon dioxide

Example Sentences

He defended crafts chain Michael’s against claims that toxic levels of carbon monoxide at one of its stores caused brain damage to an employee’s unborn daughter.

From The Wall Street Journal • Apr. 7, 2026

A rom-com need not be a sparkling shelf covered with bon-bons, but it shouldn’t be a nauseating cloud of carbon monoxide that makes you want to flee.

From The Wall Street Journal • Apr. 2, 2026

They believe carbon monoxide fumes were leaking into the cabin of the plane during Sala's flight, and the lack of an audible alarm meant Ibbotson was unable to take action to disperse the deadly gas.

From BBC • Mar. 29, 2026

The 2009 endangerment finding was the result of a major report by the EPA, which identified six greenhouse gases, including carbon monoxide and methane, as endangering current and future generations.

From BBC • Feb. 13, 2026

There are small traces of nitrogen, water vapor, argon, carbon monoxide and other gases, but the only hydrocarbons or carbohydrates present are there in less than 0.1 parts per million.

From "Cosmos" by Carl Sagan