|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
(click for larger image in new window)
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.