noun the firing pin of a breechloader.
2. plunger ·noun one who, or that which, plunges; a diver.
3. plunger ·noun a boiler in which clay is beaten by a wheel to a creamy consistence.
4. plunger ·noun one who bets heavily and recklessly on a race; a reckless speculator.
5. plunger ·noun a long solid cylinder, used, instead of a piston or bucket, as a forcer in pumps.