The Collaborative International Dictionary of English v.0.48:

Hydrazine \Hy"dra*zine\, n. [Hydr- + azo- + -ine.] (Chem.)
   Any one of a series of nitrogenous bases, resembling the
   amines and produced by the reduction of certain nitroso and
   diazo compounds; as, methyl hydrazine, phenyl hydrazine, etc.
   They are derivatives of hydrazine proper, H2N.NH2, which is
   a doubled amido group, recently (1887) isolated as a stable,
   colorless gas, with a peculiar, irritating odor. As a base it
   forms distinct salts. Called also diamide, amidogen, (or
   more properly diamidogen), etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hydrazine
    n 1: a colorless fuming corrosive liquid; a powerful reducing
         agent; used chiefly in rocket fuels