(now historical) Pertaining to or composed of nitre; having the properties of nitre, bitter.

(dentistry, automotive, informal) Nitrous oxide. / (automotive, informal) The system in some racing vehicles which pumps nitrous oxide into the engine to improve performance.

(inorganic chemistry) A non-flammable gas (N₂O) commonly used in surgery and dentistry for its anaesthetic and analgesic effects.

(inorganic chemistry) A weak acid, HNO₂, known only in solution, or as its salts and esters, the nitrites; it has a linear structure, H-O-N=O

(now historical) Air thought to be charged with nitre. / (chemistry, now historical) Nitric oxide, NO.