<p><strong>Noun:</strong></p><ul><li>A pistonlike reciprocating part moving within the cylinder of a pump or hydraulic device.</li><li>A pistonlike part in the valve of a pneumatic tire.</li><li>Also called force cup: a device consisting of a handle with a rubber suction cup at one end, used as a force pump to free clogged drains and toilet traps.</li><li>A person or thing that plunges.</li><li>A reckless bettor or speculator.</li></ul>