Ni"trous (?), a. [L. nitrosus full of natron: cf. F. nitreux. See Niter.] 1. Of, pertaining to, or containing, niter; of the quality of niter, or resembling it.

2. (Chem.) Of, pertaining to, or designating, any one of those compounds in which nitrogen has a relatively lower valence as contrasted with nitric compounds.

Nitrous acid(Chem.), a hypothetical acid of nitrogen HNO₂, not known in the free state, but forming a well known series of salts, viz., the nitrites. -- Nitrous oxide. See Laughing gas.