capper

from The Collaborative International Dictionary of English v.0.48

Capper \Cap"per\, n.
   1. One whose business is to make or sell caps.
      [1913 Webster]

   2. A by-bidder; a decoy for gamblers. [Slang, U. S.]
      [1913 Webster]

   3. An instrument for applying a percussion cap to a gun or
      cartridge.
      [1913 Webster]