nitro-

CIDE DICTIONARY

nitro-, pref. 

•  A combining form or an adjective denoting the presence of niter.  [1913 Webster]
•  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).  [1913 Webster]

Nitro group, the radical NO2; -- called also nitroxyl.

OXFORD DICTIONARY

nitro-, comb. form 1 of or containing nitric acid, nitre, or nitrogen.
2 made with or by use of any of these.
3 of or containing the monovalent -NO2 group (the nitro groups in TNT).

Etymology

Gk (as NITRE)