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.
a pumplike valve used to change the pitch in a cornet or the like.
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
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.
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Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
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
The piston rotates a crank shaft, creating movement.
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 compression ratio is a measurement of the cylinder displacement between the two extremes of the piston stroke.
From BBC ● Feb. 18, 2026
He used an explosion to drive the air out of a cylinder through a valve; then, when the hot gases cooled, a piston was sucked downwards, raising a weight.
From "The Invention of Science" by David Wootton
After a spate of big wins, Lightning is about to face his biggest race yet, competing for the Piston Cup.
From Salon ● Jun. 6, 2026
That made him look more like Piston Honda than ever.
From The Wall Street Journal ● Feb. 27, 2026
Gilgeous-Alexander had 21 points and three blocks in the half, while no Piston reached double figures.
From Seattle Times ● Nov. 7, 2022
In the U.S., levels of racial prejudice against Black people are comparable for Latinos and non-Hispanic whites, political scientists Yanna Krupnikov and Spencer Piston found in a 2016 study.
From Los Angeles Times ● Oct. 17, 2022
“It’s like an episode of Design This! All we need is Roger Piston to come in and say, ‘Do your magic!’
From "Beauty Queens" by Libba Bray
"They were equipped with a metal saw and cut through the pistons that held the frames of Renoir's works," he said.
From Barron's ● Sep. 8, 2026
If the timing chain slips or breaks—which is inevitable given enough time—the pistons will hit the valves.
From The Wall Street Journal ● Jan. 23, 2026
The technology uses the bobbing floaters to compress pistons, which push hydraulic fluid into storage tanks located nearby on land.
From Los Angeles Times ● Sep. 10, 2025
If the workings of his engine were carefully concealed, you could see the pistons pumping and sparks flying when Nadal took to court.
From BBC ● Oct. 10, 2024
They surrounded him and the fingers of their hands shot out like pistons as they questioned him.
From "The Heart is a Lonely Hunter" by Carson McCullers
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
