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.