Hyponitrous \Hy`po*ni"trous\, a. [Pref. hypo- + nitrous.] (Chem.) Containing or derived from nitrogen having a lower valence than in nitrous compounds. [1913 Webster] {Hyponitrous acid} (Chem.), an unstable nitrogen acid, {NOH}, whose salts are produced by reduction of the nitrates, although the acid itself is not isolated in the free state except as a solution in water; -- called also {nitrosylic acid}. [1913 Webster]