'Capper' definitions:

Definition of 'Capper'

From: GCIDE

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]