Isonitroso- \I`so*ni*tro"so-\ [Iso- + nitroso-.]

(Chem.) A combining from (also used adjectively), signifying: Pertaining to, or designating, the characteristic, nitrogenous radical, NOH, called the isonitroso group.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Hyponitrous \Hy`po*ni"trous\, a. [Pref. hypo- + nitrous.]

(Chem.) Containing or derived from nitrogen having a lower valence than in nitrous compounds.

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.

Source: Webster's Revised Unabridged Dictionary (1913)