Source : Webster's Revised Unabridged Dictionary (1913)

Tampion \Tam"pi*on\, n. [F. tampon, tapon, tape, of Dutch or
   German origin. See {Tap} a pipe or plug, and cf. {Tamp},
   {Tampop}, {Tompion}.] [Written also {tampeon}, and
   {tompion}.]
   1. A wooden stopper, or plug, as for a cannon or other piece
      of ordnance, when not in use.

   2. (Mus.) A plug for upper end of an organ pipe.

Source : WordNet®

tampion
     n : plug for the muzzle of a gun to keep out dust and moisture