decay

1 of 2

verb

de·​cay di-ˈkā 

decayed; decaying; decays

intransitive verb

1

: to undergo decomposition

decaying fruit

Her teeth were decaying.

… most isotopes of copper decay quickly, but two are stable: Cu-63 and Cu-65.

—David E. Thomas

2

: to decline in health, strength, or vigor

Her mind is beginning to decay with age.

believes that the moral fiber of our society is decaying

3

: to fall into ruin

the city's decaying neighborhoods

4

: to decline from a sound or prosperous condition

a decaying empire

5

: to decrease usually gradually in size, quantity, activity, or force

The three voices … decayed and died out upon her ear.

—Thomas Hardy

transitive verb

1

: to destroy by decomposition

wood decayed by bacteria

2

obsolete : to cause to decay : impair

Infirmity, that decays the wise …

—William Shakespeare

decayer noun

decay

2 of 2

noun

1

a

: rot

The material is … resistant to fire, decay and termites …

—Jack McClintock

specifically : aerobic decomposition of proteins chiefly by bacteria

b

: the product of decay

tooth decay

2

: gradual decline in strength, soundness, or prosperity or in degree of excellence or perfection

the decay of the public school system

3

: a decline in health or vigor

mental decay

4

: a wasting or wearing away : ruin

a neighborhood that had fallen into decay

5

: decrease in quantity, activity, or force: such as

a

chemistry : spontaneous decrease in the number of radioactive atoms in radioactive material

b

physics : spontaneous disintegration (as of an atom or a particle)

6

obsolete : destruction, death

… sullen presage of your own decay.

—Shakespeare

Synonyms

Verb

• rot
• decompose
• disintegrate

Noun

• deterioration
• weakening
• decaying

Choose the Right Synonym for decay

decay, decompose, rot, putrefy, spoil mean to undergo destructive dissolution.

decay implies a slow change from a state of soundness or perfection.

a decaying mansion

decompose stresses a breaking down by chemical change and when applied to organic matter a corruption.

the strong odor of decomposing vegetation

rot is a close synonym of decompose and often connotes foulness.

fruit was left to rot in warehouses

putrefy implies the rotting of animal matter and offensiveness to sight and smell.

corpses putrefying on the battlefield

spoil applies chiefly to the decomposition of foods.

keep the ham from spoiling

Examples of decay in a Sentence

Verb

the smell of decaying rubbish

dead plants and leaves decayed by bacteria

She believes that the moral fiber of our society is decaying.

our decaying public school system

The city's neighborhoods are decaying.

Noun

the decay of dead plants and leaves

She writes about the moral decay of our society.

the patient's physical and mental decay

The city's neighborhoods are in slow decay.

Recent Examples on the Web

Verb

Then, weeks after they were buried, the soft parts of the carcasses decayed and were washed away by groundwater, leaving the clay mask to forever preserve the forms of what lay just beneath, Sereno says. —Andrea Tamayo, Scientific American, 23 Oct. 2025

The decaying carcasses would have been covered by a film of bacteria, which can electrostatically attract clay found in the surrounding sediment. —Amanda Schupak, CNN Money, 23 Oct. 2025

Noun

Neutrinos were initially proposed to solve the bizarre problem of apparent energy non-conservation in nuclear (beta) decays. —Big Think, 28 Oct. 2025

At around two months to expiration, a put’s theta (time decay) is sufficient to provide meaningful daily income, while gamma (sensitivity to price changes) is low enough to prevent excessive risk from sharp short-term moves. —Michael Khouw, CNBC, 27 Oct. 2025

Word History

Etymology

Verb and Noun

Middle English, from Anglo-French decaïr, from Late Latin decadere to fall, sink, from Latin de- + cadere to fall — more at chance

First Known Use

Verb

15th century, in the meaning defined at intransitive sense 4

Noun

15th century, in the meaning defined at sense 2

Phrases Containing decay

• beta decay
• fall into decay

Rhymes for decay

• airway
• allay
• archway
• array
• ashtray
• astray
• aue
• away
• ballet
• belay
• beltway
• beret

Kids Definition

decay

1 of 2 verb

de·​cay di-ˈkā 

1

: to lose soundness, health, strength, or vigor

2

: to go through or cause to go through decomposition

a radioactive element decays

apples that decayed in storage

decay

2 of 2 noun

1

: gradual loss of strength, soundness, health, or vigor

2

: rot entry 2 sense 1

3

: a natural decrease in the number of radioactive atoms in radioactive material

Medical Definition

decay

1 of 2 intransitive verb

de·​cay di-ˈkā 

: to undergo decomposition

transitive verb

: to destroy by decomposition

decay

2 of 2 noun

1

a

: rot sense 1

specifically : aerobic decomposition of proteins chiefly by bacteria

b

: the product of decay

2

a

: spontaneous decrease in the number of radioactive atoms in radioactive material

b

: spontaneous disintegration (as of an atom or a nuclear particle)