/plun"jeuhr/ , n.
1. Mach. a pistonlike reciprocating part moving within the cylinder of a pump or hydraulic device.
2. Auto. a pistonlike part in the valve of a pneumatic tire.
3. Also called force cup, plumber's friend, plumber's helper . 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.
4. a person or thing that plunges.
5. a reckless bettor or speculator.
[ 1605-15; PLUNGE + -ER 1 ]