Source : Webster's Revised Unabridged Dictionary (1913)

Tompion \Tom"pi*on\, n. [See {Tampios}]
   1. A stopper of a cannon or a musket. See {Tampion}.

   2. (Mus.) A plug in a flute or an organ pipe, to modulate the
      tone. --Knight.

   3. The iron bottom to which grapeshot are fixed.