|a gadget; dingus; thingumbob.|
|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
|a disc or cylindrical part that slides to and fro in a hollow cylinder. In an internal-combustion engine it is forced to move by the expanding gases in the cylinder head and is attached by a pivoted connecting rod to a crankshaft or flywheel, thus converting reciprocating motion into rotation|
|[C18: via French from Old Italian pistone, from pistare to pound, grind, from Latin pinsere to crush, beat]|
|piston (pĭs'tən) Pronunciation Key
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A solid cylinder or disk that fits snugly into a hollow cylinder and moves back and forth under the pressure of a fluid (typically a hot gas formed by combustion, as in many engines), or moves or compresses a fluid, as in a pump or compressor.