Diazo- Di*az"o- [Pref. di- + azo-] (Chem.) A combining form (also used adjectively), meaning pertaining to, or derived from, a series of compounds containing a radical of two nitrogen atoms, united usually to an aromatic radical; as, diazo-benzene, C6H5.N2.OH. Note: Diazo compounds are in general unstable, but are of great importance in recent organic chemistry. They are obtained by a partial reduction of the salts of certain amido compounds. Diazo reactions (Chem.), a series of reactions whereby diazo compounds are employed in substitution. These reactions are of great importance in organic chemistry.