Plunger

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.

A boiler in which clay is beaten by a wheel to a creamy consistence.

5.

The firing pin of a breechloader.