nitric oxide

American  

noun

Chemistry.

1. a colorless, slightly water-soluble gas, NO, formed by the action of dilute nitric acid on copper, and by the direct combination of atmospheric oxygen and nitrogen at the high temperatures of an electric arc: an intermediate in the manufacture of nitric acid.

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nitric oxide British  

noun

1. Systematic name: nitrogen monoxide.  a colourless slightly soluble gas forming red fumes of nitrogen dioxide in air. Formula: NO

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nitric oxide Scientific  

1. A colorless, poisonous gas produced as an intermediate compound during the manufacture of nitric acid from ammonia or from atmospheric nitrogen. It is also produced through cellular metabolism. In the body, nitric oxide is involved in oxygen transport to the tissues, the transmission of nerve impulses, and other physiological activities. Chemical formula: NO.

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Closer Look

While nitric oxide (NO) was once regarded solely as a poisonous air pollutant, responsible for the formation of photochemical smog and acid rain leading to the destruction of the ozone layer, today it is also appreciated as a molecule essential to human health. Nitric oxide is the first gas discovered to act as a signaling molecule, a transmitter of important signals to cells in various systems of the human body. Even though NO continues to be detrimental to the environment, it was heralded as Science Magazine's Molecule of the Year in 1992, and the Nobel Prize for physiology or medicine was awarded in 1998 to the three scientists who discovered that NO works as a signaling molecule in the cardiovascular system. It is now known that the cells of a blood vessel's inner walls use NO to signal the vessel to relax and dilate, increasing blood flow. Nitroglycerin, whose effectiveness in treating heart problems was once a mystery, is now known to work by releasing NO. NO has a variety of other important biological functions, including destroying bacteria within the immune system and acting as a neurotransmitter.

Etymology

Origin of nitric oxide

First recorded in 1800–10

Example Sentences

The researchers examined how three key components interact inside brain cells: nitric oxide, the protective protein TSC2, and the mTOR pathway, which plays a central role in controlling how cells grow and produce proteins.

From Science Daily • Mar. 7, 2026

A new study focused on nitric oxide, a common chemical messenger in the brain.

From Science Daily • Mar. 7, 2026

This enzyme removes nitric oxide from proteins that regulate fat buildup.

From Science Daily • Feb. 6, 2026

The review outlines several possible mechanisms, including nitric oxide signaling that supports healthy circulation, pathways related to inflammation and oxidative stress, lipid and glucose metabolism, and interactions with the gut microbiome.

From Science Daily • Jan. 27, 2026

This gas, as we have just seen, is formed by allowing nitric oxide to come into contact with oxygen.

From An Elementary Study of Chemistry by McPherson, William