\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}.