Plunger

n.
  1. One who, or that which, plunges; a diver.
  2. A long solid cylinder, used, instead of a piston or bucket, as a forcer in pumps.
  3. One who bets heavily and recklessly on a race; a reckless speculator.
  4. (Pottery) A boiler in which clay is beaten by a wheel to a creamy consistence.
  5. (Gun.) The firing pin of a breechloader.
    6. Plunger bucket ,
    a piston, without a valve, in a pump.
    Plunger pole ,
    the pump rod of a pumping engine.
    Plunger pump ,
    a pump, as for water, having a plunger, instead of a piston, to act upon the water. It may be single-acting or double-acting