The Collaborative International Dictionary of English v.0.48:

Gunpowder \Gun"pow`der\ (g[u^]n"pou`d[~e]r), n. (Chem.)
   A black, granular, explosive substance, consisting of an
   intimate mechanical mixture of saltpeter, charcoal, and
   sulphur. It is used in gunnery and blasting.
   [1913 Webster]

   Note: Gunpowder consists of from 70 to 80 per cent of
         potassium nitraate (niter, saltpeter), 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.
         [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Explosive \Ex*plo"sive\, n.
   1. An explosive agent; a compound or mixture susceptible of a
      rapid chemical reaction, as gunpowder, TNT,
      dynamite, or nitro-glycerine.
      [1913 Webster +PJC]

   2. A sound produced by an explosive impulse of the breath;
      (Phonetics) one of consonants p, b, t, d, k, g, which are
      sounded with a sort of explosive power of voice.

   Note: [See Guide to Pronunciation, [root] 155-7, 184.]
         [1913 Webster]

WordNet (r) 3.0 (2006):

gunpowder
    n 1: a mixture of potassium nitrate, charcoal, and sulfur in a
         75:15:10 ratio which is used in gunnery, time fuses, and
         fireworks [syn: gunpowder, powder]

The Devil's Dictionary (1881-1906):

GUNPOWDER, n.  An agency employed by civilized nations for the
settlement of disputes which might become troublesome if left
unadjusted.  By most writers the invention of gunpowder is ascribed to
the Chinese, but not upon very convincing evidence.  Milton says it
was invented by the devil to dispel angels with, and this opinion
seems to derive some support from the scarcity of angels.  Moreover,
it has the hearty concurrence of the Hon. James Wilson, Secretary of
Agriculture.
    Secretary Wilson became interested in gunpowder through an event
that occurred on the Government experimental farm in the District of
Columbia.  One day, several years ago, a rogue imperfectly reverent of
the Secretary's profound attainments and personal character presented
him with a sack of gunpowder, representing it as the sed of the
_Flashawful flabbergastor_, a Patagonian cereal of great commercial
value, admirably adapted to this climate.  The good Secretary was
instructed to spill it along in a furrow and afterward inhume it with
soil.  This he at once proceeded to do, and had made a continuous line
of it all the way across a ten-acre field, when he was made to look
backward by a shout from the generous donor, who at once dropped a
lighted match into the furrow at the starting-point.  Contact with the
earth had somewhat dampened the powder, but the startled functionary
saw himself pursued by a tall moving pillar of fire and smoke and
fierce evolution.  He stood for a moment paralyzed and speechless,
then he recollected an engagement and, dropping all, absented himself
thence with such surprising celerity that to the eyes of spectators
along the route selected he appeared like a long, dim streak
prolonging itself with inconceivable rapidity through seven villages,
and audibly refusing to be comforted.  "Great Scott! what is that?"
cried a surveyor's chainman, shading his eyes and gazing at the fading
line of agriculturist which bisected his visible horizon.  "That,"
said the surveyor, carelessly glancing at the phenomenon and again
centering his attention upon his instrument, "is the Meridian of
Washington."