Plunger /(?)/

Plun·ger

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. [Cant]
  4. A boiler in which clay is beaten by a wheel to a creamy consistence. (Pottery)
  5. The firing pin of a breechloader. (Gun.)

Phrases & Compounds
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