nitro-

ni·tro-

nitro-

pref.
  1. A combining form or an adjective denoting the presence of niter.
  2. A combining form (used also adjectively) designating certain compounds of nitrogen or of its acids; as nitrohydrochloric, nitrocalcite; also, designating the group or radical NO2, or its compounds, as nitrobenzene (C6H5.NO2). (Chem.)

Phrases & Compounds
Nitro group
the radical NO2; -- called also nitroxyl.