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Webster 1913 Edition

Noun.

One whose business is to make or sell caps.

A by-bidder; a decoy for gamblers.

[Slang, U. S.]

An instrument for applying a percussion cap to a gun or cartridge.

Noun.

[from cap.] One whose business is to make or sell caps.

capper ‎(plural cappers)

One that caps.
A device or person that applies caps, as to bullets or bottles.
A person that makes or sells caps.
A finale.
- 2009, February 1, “Joe Queenan”, in Super Bowl Suits:
  The real capper is when St. John starts fawning over Hugh Hefner , host of the finest Super Bowl party known to man, musing: “The question isn’t whether Hef is the hippest octogenarian on the planet.
(US, slang, dated) A by-bidder; a decoy for gamblers.

One that caps

A device or person that applies caps, as to bullets or bottles

A person that makes or sells caps

A finale