The Collaborative International Dictionary of English v.0.48:

Powder \Pow"der\, n. [OE. poudre, pouldre, F. poudre, OF. also
   poldre, puldre, L. pulvis, pulveris: cf. pollen fine flour,
   mill dust, E. pollen. Cf. Polverine, Pulverize.]
   1. The fine particles to which any dry substance is reduced
      by pounding, grinding, or triturating, or into which it
      falls by decay; dust.
      [1913 Webster]

            Grind their bones to powder small.    --Shak.
      [1913 Webster]

   2. An explosive mixture used in gunnery, blasting, etc.;
      gunpowder. See Gunpowder.
      [1913 Webster]

   Atlas powder, Baking powder, etc. See under Atlas,
      Baking, etc.

   Powder down (Zool.), the peculiar dust, or exfoliation, of
      powder-down feathers.

   Powder-down feather (Zool.), one of a peculiar kind of
      modified feathers which sometimes form patches on certain
      parts of some birds. They have a greasy texture and a
      scaly exfoliation.

   Powder-down patch (Zool.), a tuft or patch of powder-down
      feathers.

   Powder hose, a tube of strong linen, about an inch in
      diameter, filled with powder and used in firing mines.
      --Farrow.

   Powder hoy (Naut.), a vessel specially fitted to carry
      powder for the supply of war ships. They are usually
      painted red and carry a red flag.

   Powder magazine, or Powder room. See Magazine, 2.

   Powder mine, a mine exploded by gunpowder. See Mine.

   Powder monkey (Naut.), a boy formerly employed on war
      vessels to carry powder; a powder boy.

   Powder post. See Dry rot, under Dry.

   Powder puff. See Puff, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

powder magazine
    n 1: a storehouse (as a compartment on a warship) where weapons
         and ammunition are stored [syn: magazine, powder store,
         powder magazine]