nitrogen

noun

ni·​tro·​gen ˈnī-trə-jən 

: a nonmetallic chemical element with atomic number 7 that under standard conditions is a colorless, odorless, inert gas, that constitutes 78 percent of the Earth's atmosphere, and that is used especially in the industrial synthesis of ammonia, as a component of inert atmospheres, and in liquid form as a refrigerant

—often used before another noun

the nitrogen cycle

nitrogen fertilizer

see Chemical Elements Table

Examples of nitrogen in a Sentence

Recent Examples on the Web

Heating now comes from lower-emissions heat pumps, and the existing septic system has been replaced by an Innovative/Alternative (or IA) system designed to prevent excess nitrogen and other nutrients from entering the wastewater, which contributes to water-quality issues and harmful algae blooms. —Hannah Walhout, Travel + Leisure, 4 Dec. 2025

As the plants remove nitrogen compounds and other nutrients, the purified water flows back into each aquatic zone below. —New Atlas, 3 Dec. 2025

Despite an ambitious 2025 target, growers have already achieved a 25 percent reduction in greenhouse gas (GHG) emissions by optimizing nitrogen use and adopting smarter irrigation technologies. —Sj Studio, Sourcing Journal, 2 Dec. 2025

The oxygen and nitrogen molecules also emit ultraviolet light, which can only be detected by special cameras on satellites. —Jenna Prestininzi, Freep.com, 2 Dec. 2025

Word History

Etymology

French nitrogène, from nitre niter + -gène -gen

First Known Use

1791, in the meaning defined above

Phrases Containing nitrogen

• nitrogen balance
• nitrogen cycle
• nitrogen dioxide
• nitrogen fixation
• nitrogen-fixer
• nitrogen-fixing
• nitrogen mustard
• nitrogen narcosis
• nitrogen oxide
• nitrogen tetroxide

Kids Definition

nitrogen

noun

ni·​tro·​gen ˈnī-trə-jən 

: a colorless tasteless odorless element that occurs as a gas which makes up 78 percent of the atmosphere and that forms a part of all living tissues see element

nitrogenous

nī-ˈträj-ə-nəs 

adjective

Medical Definition

nitrogen

noun

ni·​tro·​gen ˈnī-trə-jən 

: a common nonmetallic element that in the free form is normally a colorless odorless tasteless insoluble inert diatomic gas comprising 78 percent of the atmosphere by volume and that in the combined form is a constituent of biologically important compounds (as proteins, nucleic acids, and alkaloids) and hence of all living cells as well as of industrially important substances (as cyanides, fertilizers, dyes, and antibiotics)

—symbol N see Chemical Elements Table