Nitro- \Ni"tro-\

1. A combining form or an adjective denoting the presence of niter.

2. (Chem.) 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.

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

Source: Webster's Revised Unabridged Dictionary (1913)
 

Nitroxyl \Ni*trox"yl\, n. [Nitro- + oxygen + -yl.]

(Chem.) The group NO2, usually called the nitro group.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Chromophore \Chro"mo*phore\, n. [Gr. ? color + ? to bear.]

(Chem.) Any chemical group or residue (as NO2; N2; or O2) which imparts some decided color to the compound of which it is an ingredient.

Source: Webster's Revised Unabridged Dictionary (1913)