What is "plunger bucket"

Plunger \Plun"ger\, 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. [Cant]

4. (Pottery) A boiler in which clay is beaten by a wheel to a creamy consistence.
   --Knight.

5. (Gun.) The firing pin of a breechloader.

   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