- Adjective. (chemistry) of, relating to, or derived from nitrogen, especially in which the valence of the nitrogen is lower than that of a corresponding nitric species.
- Adjective. (chemistry) of, or relating to nitrous acid or its derivatives.
- Adjective. (mycology, biology) having a sharp odor like ammonia or nitric acid.
- Noun. (dentistry, informal) Nitrous oxide.