nitrous (adj.)youdaoicibaDictYouDict[nitrous 词源字典]
c. 1600, from Latin nitrosus, from nitrum (see nitre). Originally "of nitre, pertaining to nitre;" more precise use in chemistry (designating a compound in which the nitrogen has a lower valence than the corresponding nitric compound) is from 1780s. Nitrous oxide attested from 1800.[nitrous etymology, nitrous origin, 英语词源]