deceleration
Americannoun
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the fact of losing speed, or the act of reducing the speed of something.
Prolonged deceleration of the fetal heart rate is cause for concern.
-
the act or process of slowing the rate of increase of something.
During that quarter, job creation stalled and stocks fell, confirming that there was a deceleration in the economy.
Usage
What does deceleration mean? Deceleration describes a decrease in velocity, that is, momentum. Deceleration describes the slowing of an increase. Wind, for example, moves with a certain amount of momentum. When the wind’s momentum slows down, that is, the wind doesn’t blow as hard, we can say that the wind is experiencing deceleration. Example: The deceleration of the ship came abruptly to the passengers.
Other Word Forms
Etymology
Origin of deceleration
Explanation
Deceleration is a slowing down: the unexpected deceleration of your car might mean that you've run out of gas. Use the noun deceleration when you talk about a gradual decrease in speed. When you're on a Ferris wheel, its deceleration tells you that the ride is almost over, and the deceleration of a train at a railroad crossing happens for safety reasons. The opposite of deceleration is acceleration, or speeding up. The word deceleration was originally an 1890's railroad term, constructed by adding de, or "the opposite of" to acceleration.
Vocabulary lists containing deceleration
Force and Motion (Mechanics) - Middle School
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Force and Motion (Mechanics) - Introductory
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Physics - Introductory
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
At lower energies, nuclear stopping initially slows the matter down, producing deceleration of up to about 500 MeV.
From Science Daily ● Aug. 3, 2026
It was a sharp deceleration from May’s 1% gain.
From The Wall Street Journal ● Jul. 16, 2026
What that looks like is double- and triple-digit earnings growth for the energy and information-technology sectors but “notable” deceleration for financials and industrials, from 20%-plus in the first quarter to a high-single-digit percentage, they said.
From MarketWatch ● Jul. 10, 2026
The report indicates that "Engine 1's core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration…".
From BBC ● Jun. 10, 2026
I did some basic acceleration and deceleration, turned in increasingly tight circles, and even did a power-stop.
From "The Martian" by Andy Weir
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.
