decay

American  

[dih-key] / dɪˈkeɪ /

verb (used without object)

1. to become decomposed; rot.

   vegetation that was decaying.

   Synonyms:

   putrefy, wither, degenerate

2. to decline in excellence, prosperity, health, etc.; deteriorate.

3. 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)

1. to cause to decay or decompose; rot.

   The dampness of the climate decayed the books.

noun

1. decomposition; rot.

   Decay made the wood unsuitable for use.

   Synonyms:

   putrefaction

2. a gradual falling into an inferior condition; progressive decline.

   the decay of international relations; the decay of the Aztec civilizations.

3. decline in or loss of strength, health, intellect, etc..

   His mental decay is distressing.

   Synonyms:

   degeneration, dilapidation, impairment, decadence, deterioration

4. Physics. radioactive decay.

5. Aerospace. the progressive, accelerating reduction in orbital parameters, particularly apogee and perigee, of a spacecraft due to atmospheric drag.

decay British  

/ dɪˈkeɪ /

verb

1. to decline or cause to decline gradually in health, prosperity, excellence, etc; deteriorate; waste away

2. to rot or cause to rot as a result of bacterial, fungal, or chemical action; decompose

3. Also: disintegrate.  (intr) physics

   1. (of an atomic nucleus) to undergo radioactive disintegration

   2. (of an elementary particle) to transform into two or more different elementary particles

4. (intr) physics (of a stored charge, magnetic flux, etc) to decrease gradually when the source of energy has been removed

---

noun

1. the process of decline, as in health, mentality, beauty, etc

2. the state brought about by this process

3. decomposition, as of vegetable matter

4. rotten or decayed matter

   the dentist drilled out the decay

5. physics

   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

6. physics a gradual decrease of a stored charge, magnetic flux, current, etc, when the source of energy has been removed See also time constant

7. music the fading away of a note

decay Scientific  

/ dĭ-kā′ /

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.

3. See more at fundamental force radioactive decay

---

1. To undergo decay.

Related Words

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

• decayable
  adjective
• decayedness
  adjective
• decayless
  adjective
• nondecayed
  adjective
• nondecaying
  adjective
• redecay
  verb
• semidecay
  noun
• semidecayed
  adjective
• undecayable
  adjective
• undecayed
  adjective
• undecaying
  adjective

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.

Example Sentences

The team plans to carry out further experiments to improve measurement accuracy and look for additional decay signals that could confirm the existence of η′-mesic nuclei.

From Science Daily • Apr. 25, 2026

We began to roll past dead and dying trees in various stages of decay.

From Slate • Apr. 20, 2026

His lines are lazy, woozy, all-forgiving reportage about the seasons’ slow parade, the meandering ongoingness of our world: arrival, decay and the modest glory in between.

From The Wall Street Journal • Apr. 16, 2026

This limits event risk and harnesses time decay, the term for how options lose value each day closer to expiration.

From Barron's • Apr. 8, 2026

The ’dobe house had entered its second decay.

From "East of Eden" by John Steinbeck

Related Words

• atrophy
• corrode
• decompose
• degenerate
• discolor
• disintegrate
• dissolve
• dwindle
• fade
• get worse
• lessen
• mortify
• pollute
• rot
• shrivel
• wane
• wither