What is the meaning of Nitrous?

Pertaining to or composed of nitre; having the properties of nitre, bitter.

Of, relating to, or derived from nitrogen, especially in which the valence of the nitrogen is lower than that of a corresponding nitric species.

Of or relating to nitrous acid or its derivatives.

Having a sharp odor like ammonia or nitric acid.

Nitrous oxide.

The system in some racing vehicles which pumps nitrous oxide into the engine to improve performance.

Source: wiktionary.org