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:
Enamel damage is one of the major factors behind tooth decay and other dental conditions that affect almost 50% of the global population.
From Science Daily ● Jul. 23, 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
But when a 2024 reserve study and subsequent inspections revealed extensive structural decay, the association was faced with a $600,000 repair bill, according to a report from the Foundation for Community Association Research.
From MarketWatch ● Jul. 7, 2026
Berlin has let regulations, labor costs, energy prices and taxes creep up and its infrastructure decay due to underinvestment over the past 20 years, eroding the economy’s competitiveness.
From The Wall Street Journal ● Jul. 2, 2026
To begin with, it was discovered that one of the basic components of Libby’s formula, known as the decay constant, was off by about 3 percent.
From "A Short History of Nearly Everything" by Bill Bryson
The research team focused on detecting moments when a high-energy neutrino hits a carbon-13 nucleus and converts it into nitrogen-13, a radioactive form of nitrogen that decays roughly ten minutes later.
From Science Daily ● Dec. 12, 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
It gets creaky and decays, eventually becoming tasty sustenance for worms.
From Los Angeles Times ● Jan. 7, 2025
When a subatomic particle travels very fast, it survives longer than expected before it decays, because its clock is slow.
From "Zero: The Biography of a Dangerous Idea" by Charles Seife
“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
Greiff points out baby heather plants nearby now able to grow in gaps left by decayed moss.
From BBC ● May 30, 2026
As the animal decayed hundreds of millions of years ago, its body changed in ways that later made it resemble an octopus when preserved in rock.
From Science Daily ● Apr. 7, 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
And ever since that day the race of Númenor has decayed, and the span of their years has lessened.
From "The Fellowship of the Ring" by J.R.R. Tolkien
Officials say some 1,800 localities have already vanished since the turn of the century -- ghost villages that have become nothing more than decaying buildings and a name on a map.
From Barron's ● Jul. 22, 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
The space, which stretches as far as the eye can see, looks like an office, a showroom, a library and a decaying home all at once.
From Salon ● May 30, 2026
The ground beneath them was a bank covered with coarse grass, torn everywhere by the upheavals of fallen trees, scattered with decaying coconuts and palm saplings.
From "Lord of the Flies" by William Golding
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.
