plunger

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who plunges or dives.
• noun A device consisting of a rubber suction cup attached to the end of a stick, used to unclog drains and pipes.
• noun A part of a machine, tool, or device that operates wtih a thrusting or plunging movement, such as a piston.

from The Century Dictionary.

• noun One who or that which plunges.
• noun A cavalryman; in the plural, cavalry.
• noun A reckless better; a dashing or venturesome gambler or speculator.
• noun A part of a machine or piece of mechanism that plunges. , , ,
• noun In pottery, a vessel in which clay is beaten by a wheel to the required consistency.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, plunges; a diver.
• noun A long solid cylinder, used, instead of a piston or bucket, as a forcer in pumps.
• noun Cant One who bets heavily and recklessly on a race; a reckless speculator.
• noun (Pottery) A boiler in which clay is beaten by a wheel to a creamy consistence.
• noun (Gun.) The firing pin of a breechloader.
• noun a piston, without a valve, in a pump.
• noun the pump rod of a pumping engine.
• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A device that is used to remove blockages from a toilet or sink by suction.
• noun The internal piece of a syringe that pushes out or pulls in any contents.
• noun The sliding activator of an exploder, an electrical generator used to trigger electrical detonators such as blasting caps.
• noun The part of a cafetière that is pushed down to remove grounds from coffee.
• noun One who plunges; a diver.
• noun A device similar to a piston but without a mechanism; a long solid cylinder used, instead of a piston or bucket, as a forcer in pumps.
• noun The moving portion of solenoid.
• noun pinball The spring-loaded assembly that propels the ball onto the table.
• noun dated, slang A reckless gambler.
• noun pottery A boiler in which clay is beaten by a wheel to a creamy consistency.
• noun firearms The firing pin of a breechloader.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun hand tool consisting of a stick with a rubber suction cup at one end; used to clean clogged drains
• noun someone who risks losses for the possibility of considerable gains
• noun mechanical device that has a plunging or thrusting motion
• noun someone who dives (into water)