decay
Americanverb (used without object)
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to become decomposed; rot.
vegetation that was decaying.
- Synonyms:
- putrefy, wither, degenerate
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to decline in excellence, prosperity, health, etc.; deteriorate.
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Physics. (of a radioactive nucleus) to change spontaneously into one or more different nuclei in a process in which atomic particles, as alpha particles, are emitted from the nucleus, electrons are captured or lost, or fission takes place.
verb (used with object)
noun
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Decay made the wood unsuitable for use.
- Synonyms:
- putrefaction
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a gradual falling into an inferior condition; progressive decline.
the decay of international relations; the decay of the Aztec civilizations.
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decline in or loss of strength, health, intellect, etc..
His mental decay is distressing.
- Synonyms:
- degeneration, dilapidation, impairment, decadence, deterioration
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Physics. radioactive decay.
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Aerospace. the progressive, accelerating reduction in orbital parameters, particularly apogee and perigee, of a spacecraft due to atmospheric drag.
verb
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to decline or cause to decline gradually in health, prosperity, excellence, etc; deteriorate; waste away
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to rot or cause to rot as a result of bacterial, fungal, or chemical action; decompose
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Also: disintegrate. (intr) physics
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(of an atomic nucleus) to undergo radioactive disintegration
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(of an elementary particle) to transform into two or more different elementary particles
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(intr) physics (of a stored charge, magnetic flux, etc) to decrease gradually when the source of energy has been removed
noun
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the process of decline, as in health, mentality, beauty, etc
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the state brought about by this process
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decomposition, as of vegetable matter
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rotten or decayed matter
the dentist drilled out the decay
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physics
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a spontaneous transformation of an elementary particle into two or more different particles
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of an excited atom or molecule, losing energy by the spontaneous emission of photons
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physics a gradual decrease of a stored charge, magnetic flux, current, etc, when the source of energy has been removed See also time constant
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music the fading away of a note
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The breaking down or rotting of organic matter through the action of bacteria, fungi, or other organisms; decomposition.
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The spontaneous transformation of a relatively unstable particle into a set of new particles. For example, a pion decays spontaneously into a muon and an antineutrino. The decay of heavy or unstable atomic nuclei (such as uranium or carbon-10) into more stable nuclei and emitted particles is called radioactive decay. The study of particle decay is fundamental to subatomic physics.
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See more at fundamental force radioactive decay
Synonym Usage
Decay, decompose, disintegrate, rot imply a deterioration or falling away from a sound condition. Decay implies either entire or partial deterioration by progressive natural changes: Teeth decay. Decompose suggests the reducing of a substance to its component elements: Moisture makes some chemical compounds decompose. Disintegrate emphasizes the breaking up, going to pieces, or wearing away of anything, so that its original wholeness is impaired: Rocks disintegrate. Rot is a stronger word than decay and is especially applied to decaying vegetable matter, which may or may not emit offensive odors: Potatoes rot.
Other Word Forms
Derived Forms
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semidecaynoun
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redecayverb
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decayableadjective
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decayednessadjective
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decaylessadjective
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nondecayedadjective
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nondecayingadjective
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semidecayedadjective
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undecayableadjective
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undecayedadjective
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undecayingadjective
Inflected Forms
Participles
Conjugated Forms
Present
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decaysimple
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decayssimple
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have decayedperfect
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has decayedperfect
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am decayingprogressive
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are decayingprogressive
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is decayingprogressive
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have been decayingperfect progressive
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has been decayingperfect progressive
Past
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decayedsimple
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had decayedperfect
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was decayingprogressive
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were decayingprogressive
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had been decayingperfect progressive
Future
Etymology
Origin of decay
First recorded in 1425–75; late Middle English verb decayen, decaien, from Old North French decair, equivalent to de- “down” + cair “to fall,” from unattested Vulgar Latin cadēre, for Latin cadere; noun derivative of the verb; see de-.
Explanation
To decay means to rot, decompose, break down. Our bodies—anything organic—will decay after death. Broken sidewalks, potholes, graffiti are all signs of urban decay. Tooth decay is something to avoid. Decay can also mean decline. Anyone, even a great athlete, must exercise regularly to maintain muscle tone—as soon as you stop, the muscles begin to decay. If the strength of the cable signal coming into your house grows weaker over time, you can complain that it has decayed.
Vocabulary lists containing decay
Earth Science - Middle School
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Rocks and Minerals - Introductory
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Earth Science: Natural Resources and the Environment
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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.
See Examples For:
Tooth decay is the most common chronic disease among children and affects more than 40% of children in the United States.
From Science Daily ● Jul. 29, 2026
In 1993, he coordinated businessman Richard Riordan’s successful campaign for Los Angeles mayor by targeting homeowners’ anxieties about unemployment, crime and other symptoms of urban decay.
From Los Angeles Times ● Jul. 22, 2026
Cuban-Americans seeking their old properties often find the buildings in decay.
From The Wall Street Journal ● Jul. 22, 2026
"Suddenly when they're out of the ground, they're out of equilibrium, and that normally means they start to decay, fall apart."
From BBC ● Jul. 11, 2026
Then the house, or hut, was left to decay.
From "A Girl Named Disaster" by Nancy Farmer
Sphagnum moss can hold 20 times its weight in water and helps create peat bogs, where dead vegetation accumulates rather than decays, capturing carbon in the ground.
From BBC ● Feb. 8, 2026
When astatine decays, it emits alpha particles -- tiny clusters made of two protons and two neutrons -- that can release powerful, localized bursts of energy.
From Science Daily ● Nov. 11, 2025
It contains radium that decays into radon gas, which is radioactive and can cause cancer.
From Barron's ● Oct. 10, 2025
Keeping the truth from someone might not be outright dishonesty, but it’s a rot that decays the same way, just festering at a slower pace.
From Salon ● Apr. 18, 2025
Like hydrogen-7 or lithium-5 or boron-7, love has an infinitesimally small half-life that decays to nothing.
From "The Sun Is Also a Star" by Nicola Yoon
“Remote and hybrid work used to be a privilege, but its benefits over in-person work have decayed across the board,” Chris Martin, senior economist at Glassdoor, told MarketWatch.
From MarketWatch ● Jun. 27, 2026
Pyne added the tree would not immediately disappear, and as it decayed over the next few decades, would provide a home to many animals and plants.
From BBC ● Jun. 17, 2026
In several cases, these concretions sealed off the interior lining, preserving pieces of fabric that would normally have decayed long ago.
From Science Daily ● Jun. 8, 2026
In “Vaccine Flag,” a vertical banner arcs gracefully across a soft gradient of L.A. haze, but the banner’s fabric is so tattered and decayed that its advertisement for vaccines is barely legible.
From Los Angeles Times ● Feb. 16, 2026
He finished, and his last notes decayed into silence.
From "The Serpent King" by Jeff Zentner
On the shore of a nondescript, decaying seaside town, a boat that went missing 30 years ago suddenly reappears.
From Los Angeles Times ● Jun. 19, 2026
The ornate stone balconies of the decaying colonial townhouses jutting above your head are liable to collapse at any moment.
From Barron's ● Jun. 17, 2026
According to Marek, millipedes were among the early pioneers of life on land, helping recycle nutrients by feeding on decaying organic material in some of the first terrestrial ecosystems.
From Science Daily ● Jun. 14, 2026
NEW YORK—More than a million fans will visit New York City this month for the World Cup, and many of them will squeeze through the decaying bowels of Pennsylvania Station while they’re here.
From The Wall Street Journal ● Jun. 13, 2026
I presented her with the two red leaf beetles I’d managed to find under a decaying log.
From "Willodeen" by Katherine Applegate
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.
