Nitrobenzene \Ni`tro*ben"zene\ (? or ?), n. [Nitro- + benzene.]
   (Chem.)
   A yellow aromatic liquid (C6H5.NO2), produced by the action
   of nitric acid on benzene, and called from its odor
   imitation oil of bitter almonds, or essence of mirbane.
   It is used in perfumery, and is manufactured in large
   quantities in the preparation of aniline. Fornerly called
   also nitrobenzol.
   [1913 Webster] Nitrobenzol

nitro- \ni"tro-\pref.
   1. A combining form or an adjective denoting the presence of
      niter.
      [1913 Webster]

   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
      (C6H5.NO2).
      [1913 Webster]

   Nitro group, the radical NO2; -- called also nitroxyl.
      [1913 Webster]

niacin \niacin\ n.
   A B vitamin (vitamin B5) essential for the normal function of
   the nervous system and the gastrointestinal tract. Called
   also nicotinic acid and antipellagra vitamin. Chemical
   formula C6H5NO2, chemically it is 3-pyridinecarboxylic
   acid.

   Syn: nicotinic acid.
        [WordNet 1.5]

nicotinic acid \nic`o*tin"ic ac"id\, n. (Chem.)
   An organic acid (C6H5NO2), a carboxylated derivative of
   pyridine, obtained by the oxidation of nicotine; called also
   niacin and antipellagra vitamin, and vitamin B5.
   Chemically it is 3-pyridinecarboxylic acid.

   Note: It is a cofactor in several enzymatic reactions, and is
         used to prevent a pellagra-like disease in dogs.
         --[MI11]

   Syn: 3-pyridinecarboxylic acid, niacin, antipellagra vitamin.
        [1913 Webster +PJC]