A solid cylinder or disk that fits snugly into a larger cylinder and moves under fluid pressure, as in a reciprocating engine, or displaces or compresses fluids, as in pumps and compressors.
Music A valve mechanism in brass instruments for altering the pitch.
[French, from Italian pistone, pestone, large pestle, from pestare, to pound, crush, from Late Latin pistāre, frequentative of Latin pīnsere, pīnsāre.]
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