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• piston
  piston

  noun

  a disk or cylindrical part tightly fitting and moving within a cylinder, either to compress or move a fluid collected in the cylinder, as air or water, or to transform energy imparted by a fluid entering or expanding inside the cylinder, as compressed air, explosive gases, or steam, into a rectilinear motion usually transformed into rotary motion by means of a connecting rod.
• Piston
  Piston

  noun

  Walter, 1894–1976, U.S. composer.

piston

¹ American  

[pis-tuhn] / ˈpɪs tən /

noun

1. a disk or cylindrical part tightly fitting and moving within a cylinder, either to compress or move a fluid collected in the cylinder, as air or water, or to transform energy imparted by a fluid entering or expanding inside the cylinder, as compressed air, explosive gases, or steam, into a rectilinear motion usually transformed into rotary motion by means of a connecting rod.

2. a pumplike valve used to change the pitch in a cornet or the like.

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Piston ² American  

[pis-tuhn] / ˈpɪs tən /

noun

1. Walter, 1894–1976, U.S. composer.

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piston British  

/ ˈpɪstən /

noun

1. 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

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piston Scientific  

/ pĭs′tən /

1. 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.

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Other Word Forms

• pistonlike
  adjective
• subpiston
  noun

Etymology

Origin of piston

First recorded in 1695–1705; from French, from Italian pistone “piston,” a learned alteration of pestone “large pestle,” equivalent to pest(are) “to pound” (variant of Medieval Latin pistare, derivative of Latin pīstus, past participle of pīnsere “to pound, crush”) + -one augmentative suffix

Explanation

A piston is a part of an engine that moves up and down inside a cylinder. Pistons help propel a vehicle by pushing fuel and air into a small space, where a spark plug can ignite and get things moving. A piston is a small but vital element in a complicated machine. Lawnmowers and motorcycles can have one piston or as many as 12. Most cars have four, six, or eight pistons. The exact way pistons work depends on the specific type of engine, but they're always essential. The word itself comes from the piston's repetitive movement — it shares a root meaning of "to pound" with pestle, the tool used for pounding and grinding spices.

Example Sentences

Alexander Shkolnik is founder of LiquidPiston, a company attempting a nearly impossible feat: developing a liquid-fuel-powered alternative to the traditional piston engine.

From The Wall Street Journal • Apr. 24, 2026

A spark ignites a fuel-air mix, pushing down the piston.

From The Wall Street Journal • Apr. 24, 2026

Wankel’s engine is legendary among engineers and gearheads, on account of its simplicity and elegance: It has far fewer parts than a typical piston engine.

From The Wall Street Journal • Apr. 24, 2026

The temperature contrast drives a piston, which in turn produces mechanical energy.

From Science Daily • Feb. 27, 2026

The bottom of the tube was placed in the water, so when the piston was raised, the water level followed the plunger upward.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife

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