[ dih-key ]
See synonyms for: decaydecayeddecaying on

verb (used without object)
  1. to become decomposed; rot: vegetation that was decaying.

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

  1. 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.

  1. decomposition; rot: Decay made the wood unsuitable for use.

  2. a gradual falling into an inferior condition; progressive decline: the decay of international relations; the decay of the Aztec civilizations.

  1. decline in or loss of strength, health, intellect, etc.: His mental decay is distressing.

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

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-.

synonym study For decay

1. 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 words for decay

Other words from decay

  • de·cay·a·ble, adjective
  • de·cayed·ness [dih-keyd-nis, -key-id-], /dɪˈkeɪd nɪs, -ˈkeɪ ɪd-/, adjective
  • de·cay·less, adjective
  • non·de·cayed, adjective
  • non·de·cay·ing, adjective
  • re·de·cay, verb
  • sem·i·de·cay, noun
  • sem·i·de·cayed, adjective
  • un·de·cay·a·ble, adjective
  • un·de·cayed, adjective
  • un·de·cay·ing, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use decay in a sentence

British Dictionary definitions for decay


/ (dɪˈkeɪ) /

  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

  1. Also: disintegrate (intr) physics

    • (of an atomic nucleus) to undergo radioactive disintegration

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

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

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

  2. the state brought about by this process

  1. decomposition, as of vegetable matter

  2. rotten or decayed matter: the dentist drilled out the decay

  3. physics

    • a spontaneous transformation of an elementary particle into two or more different particles

    • of an excited atom or molecule, losing energy by the spontaneous emission of photons

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

  5. music the fading away of a note

Origin of decay

C15: from Old Northern French decaïr, from Late Latin dēcadere, literally: to fall away, from Latin cadere to fall

Derived forms of decay

  • decayable, adjective

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

Scientific definitions for decay


[ 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. See more at fundamental force radioactive decay.

  1. To undergo decay.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.