plunger

noun

1. 1.A device that is used to remove blockages from the drain of a basin or tub, by suction.
2. 2.The internal piece of a syringe that pushes out or pulls in any contents.
3. 3.The sliding activator of an exploder, an electrical generator used to trigger electrical detonators such as blasting caps.
4. 4.The part of a cafetière that is pushed down to remove grounds from coffee.
5. 5.One who plunges; a diver.