The Collaborative International Dictionary of English v.0.48:

Nitrite \Ni"trite\, n. [Cf. F. nitrite. See Niter.] (Chem.)
   A salt or ester of nitrous acid; a compound bearing the
   -NO2 radical.
   [1913 Webster +PJC]

   Amyl nitrite, a yellow oily volatile liquid, used in
      medicine as a depressant and a vaso-dilator. Its
      inhalation produces an instantaneous flushing of the face.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nitrite
    n 1: the radical -NO2 or any compound containing it (such as a
         salt or ester of nitrous acid)