Definition
A colorless, odorless, tasteless gas that makes up about 78 percent of the Earth's atmosphere by volume. Nitrogen is chemically inert under normal atmospheric conditions and does not support combustion.
Plain English
The most common gas in the air around us. It does not burn and does not react easily with other substances. Roughly four out of every five molecules of air are nitrogen.
Context Anchor
Seen in atmosphere discussions when describing what air is made of and why the effect of breathing air changes with altitude.
Derivation
From the Greek 'nitron' (a type of mineral salt) and 'gen' (forming or producing). It was named in the 1790s for its role in forming nitre. Knowing this is mainly trivia for pilots — the practical point is that nitrogen is a normal, harmless component of the air.
Why Pilots Care
Knowing nitrogen forms the bulk of the atmosphere helps explain why total air pressure and density drop predictably with altitude, directly affecting aircraft performance and instrument indications.
Grounding Statement
At any normal altitude, most of the air molecules around the airplane are nitrogen molecules.
Intuition Check
Do not confuse “most of the air” with “most important for breathing.” Nitrogen is the largest part of air, but oxygen is the part your body depends on most during flight.
Example Sentence 1
The atmosphere is roughly 78 percent nitrogen and 21 percent oxygen, with trace amounts of other gases.
Example Sentence 2
Because nitrogen is inert, it does not participate in the combustion process inside an aircraft engine.