Definition of piston
1
: a sliding piece moved by or moving against fluid pressure which usually consists of a short cylindrical body fitting within a cylindrical chamber or vessel along which it moves back and forth
2
: a sliding valve moving in a cylinder in a brass instrument which when depressed by a finger knob serves to lower the instrument's pitch
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Merriam-Webster unabridged
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Time Traveler for piston
The first known use of piston was in 1704
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