plunger

n. 1. One who, or that which, plunges; a diver. [ 1913 Webster ]

2. A long solid cylinder, used, instead of a piston or bucket, as a forcer in pumps. [ 1913 Webster ]

3. One who bets heavily and recklessly on a race; a reckless speculator. [ Cant ] [ 1913 Webster ]

4. (Pottery) A boiler in which clay is beaten by a wheel to a creamy consistence. Knight. [ 1913 Webster ]

5. (Gun.) The firing pin of a breechloader. [ 1913 Webster ]

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 [ 1913 Webster ]