nitrous adj.

c. 1600, "of nitre, pertaining to nitre," from Latin nitrosus, from nitrum (see nitre). The more precise use in chemistry (designating a compound in which the nitrogen has a lower valence than the corresponding nitric compound) is from 1780s. Middle English had nitrose "nitrous in quality; bitter, sour" (early 15c.). Nitrous oxide "laughing gas" is attested from 1800.

When inhaled it produces unconsciousness and insensibility to pain; hence it is used as an anesthetic during short surgical operations. When it is breathed diluted with air an exhilarating or intoxicating effect is produced under the influence of which the inhaler is irresistibly impelled to do all kinds of silly and extravagant acts; hence the old name of laughing-gas. [Century Dictionary, 1895]