Source : Webster's Revised Unabridged Dictionary (1913)

Gunpowder \Gun"pow`der\, n. (Chem.)
   A black, granular, explosive substance, consisting of an
   intimate mechanical mixture of niter, charcoal, and sulphur.
   It is used in gunnery and blasting.

   Note: Gunpowder consists of from 70 to 80 per cent of niter,
         with 10 to 15 per cent of each of the other
         ingredients. Its explosive energy is due to the fact
         that it contains the necessary amount of oxygen for its
         own combustion, and liberates gases (chiefly nitrogen
         and carbon dioxide), which occupy a thousand or fifteen
         hundred times more space than the powder which
         generated them.

   {Gunpowder pile driver}, a pile driver, the hammer of which
      is thrown up by the explosion of gunpowder.

   {Gunpowder plot} (Eng. Hist.), a plot to destroy the King,
      Lords, and Commons, in revenge for the penal laws against
      Catholics. As Guy Fawkes, the agent of the conspirators,
      was about to fire the mine, which was placed under the
      House of Lords, he was seized, Nov. 5, 1605. Hence, Nov. 5
      is known in England as {Guy Fawkes Day}.

   {Gunpowder tea}, a species of fine green tea, each leaf of
      which is rolled into a small ball or pellet.

Source : WordNet®

Gunpowder Plot
     n : a conspiracy in 1605 in England to blow up James I and the
         Houses of Parliament to avenge the persecution of
         Catholics in England; led by Guy Fawkes