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[dih-key] /dɪˈkeɪ/
verb (used without object)
to become decomposed; rot:
vegetation that was decaying.
to decline in excellence, prosperity, health, etc.; deteriorate.
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)
to cause to decay or decompose; rot:
The dampness of the climate decayed the books.
decomposition; rot:
Decay made the wood unsuitable for use.
a gradual falling into an inferior condition; progressive decline:
the decay of international relations; the decay of the Aztec civilizations.
decline in or loss of strength, health, intellect, etc.:
His mental decay is distressing.
Also called disintegration, radioactive decay. Physics. a radioactive process in which a nucleus undergoes spontaneous transformation into one or more different nuclei and simultaneously emits radiation, loses electrons, or undergoes fission.
Aerospace. the progressive, accelerating reduction in orbital parameters, particularly apogee and perigee, of a spacecraft due to atmospheric drag.
Origin of decay
late Middle English
1425-75; (v.) late Middle English decayen < Old North French decair, equivalent to de- de- + cair to fall < Vulgar Latin *cadēre, for Latin cadere; (noun) late Middle English, derivative of the v.
Related forms
decayable, adjective
[dih-keyd-nis, -key-id-] /dɪˈkeɪd nɪs, -ˈkeɪ ɪd-/ (Show IPA),
decayless, adjective
nondecayed, adjective
nondecaying, adjective
redecay, verb
semidecay, noun
semidecayed, adjective
undecayable, adjective
undecayed, adjective
undecaying, adjective
1. degenerate, wither; putrefy. 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. 5. putrefaction. 7. deterioration, decadence, impairment, dilapidation, degeneration. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for decay
Contemporary Examples
Historical Examples
  • In either case they decay as soon as their work is accomplished.

    Field and Woodland Plants William S. Furneaux
  • She was aware of the creeping fret, the poisons and obstructions of decay.

  • As this also occurs in early autumn, I suppose it to be occasioned by the decay of some of the leaves.

    Wood and Garden Gertrude Jekyll
  • Will you have nothing to remember him by but his ruin and decay?

    Little Dorrit Charles Dickens
  • The symptoms of decay, which not even the wise rule of Theodosius had been able to remove, had grown more alarming.

    The World's Greatest Books, Vol XI. Edited by Arthur Mee and J.A. Hammerton
British Dictionary definitions for decay


to decline or cause to decline gradually in health, prosperity, excellence, etc; deteriorate; waste away
to rot or cause to rot as a result of bacterial, fungal, or chemical action; decompose
(intransitive) (physics) Also disintegrate
  1. (of an atomic nucleus) to undergo radioactive disintegration
  2. (of an elementary particle) to transform into two or more different elementary particles
(intransitive) (physics) (of a stored charge, magnetic flux, etc) to decrease gradually when the source of energy has been removed
the process of decline, as in health, mentality, beauty, etc
the state brought about by this process
decomposition, as of vegetable matter
rotten or decayed matter: the dentist drilled out the decay
  1. See radioactive decay
  2. a spontaneous transformation of an elementary particle into two or more different particles
  3. of an excited atom or molecule, losing energy by the spontaneous emission of photons
(physics) a gradual decrease of a stored charge, magnetic flux, current, etc, when the source of energy has been removed See also time constant
(music) the fading away of a note
Derived Forms
decayable, adjective
Word Origin
C15: from Old Northern French decaïr, from Late Latin dēcadere, literally: to fall away, from Latin cadere to fall
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for decay

late 15c., "to decrease," from Anglo-French decair, Old North French decair (Old French decheoir, 12c., Modern French déchoir) "to fall, set (of the sun), weaken, decline, decay," from Vulgar Latin *decadere "to fall off," from de- (see de-) + Latin cadere "to fall" (see case (n.1)). Meaning "decline, deteriorate" is c.1500; that of "to decompose, rot" is from 1570s. Related: Decayed; decaying.


mid-15c., "deterioration, decline in value," from decay (v.). Meaning "gradual decrease in radioactivity" is from 1897.

Online Etymology Dictionary, © 2010 Douglas Harper
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decay in Medicine

decay de·cay (dĭ-kā')

  1. The destruction or decomposition of organic matter as a result of bacterial or fungal action; rot.

  2. Dental caries.

  3. The loss of information that was registered by the senses and processed into the short-term memory system.

  4. Radioactive decay.

v. de·cayed, de·cay·ing, de·cays
  1. To break down into component parts; rot.

  2. To disintegrate or diminish by radioactive decay.

  3. To decline in health or vigor; waste away.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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decay in Science
  1. The breaking down or rotting of organic matter through the action of bacteria, fungi, or other organisms; decomposition.

  2. 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. See more at fundamental force, radioactive decay.

Verb  To undergo decay.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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decay in Technology

[Nuclear physics] An automatic conversion which is applied to most array-valued expressions in C; they "decay into" pointer-valued expressions pointing to the array's first element. This term is not used in the official standard for the language.
[Jargon File]

The Free On-line Dictionary of Computing, © Denis Howe 2010
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