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

Because their rivals believe they have found a way of exploiting the rule restricting the compression ratio - a measurement of the cylinder displacement between the two extremes of the piston stroke - to 16:1.

From BBC • Feb. 20, 2026

The higher forces, in turn, would require thicker piston crowns, shortened connecting rods and thicker wrist pins.

From The Wall Street Journal • Feb. 12, 2026

Flowing spaces open with double-height spaces, subtle level changes and large openings like skylights, clerestory windows, balconies, and even a spot where an entire section of roof pivots open thanks to a large piston.

From Los Angeles Times • Sep. 8, 2025

The piston cores were taken inside pockmarks and at background sites adjacent to but outside of the pockmarks for comparison.

From Science Daily • May 21, 2024

In addition, he needed a technique for having the valves in the piston open and close by the action of the machine itself.

From "The Invention of Science" by David Wootton

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