decay

decay — verb

1. to become gradually weaker, more damaged, or less effective over time, or to cau

1.verbtransitive / intransitiveB1
Definition

to become gradually weaker, more damaged, or less effective over time, or to cause this to happen. For example, a tooth decays when acid breaks down the enamel, a building decays when no one repairs it, or a relationship decays when trust erodes.

Example

The wooden fence had begun to decay after years of rain and sun.

intransitive: [material] + decay after + [conditions]

If you do not brush your teeth every day, they will decay and hurt.

Common collocations
  • decay slowly
  • decay rapidly
  • begin to decay
  • left to decay
Synonyms
  • rot

    more specific to organic material breaking down, often with a smell

  • deteriorate

    more formal; can apply to abilities, conditions, or situations

  • decompose

    technical term for organic matter breaking down chemically

  • decline

    focuses on losing quality or strength rather than physical damage

Antonyms

Grammar Patterns

decay (intransitive): [subject] decays

decay + noun phrase (transitive): [agent] decays [object]

Usage Note

Commonly used without a direct object (intransitive). The transitive form ('Something decays something else') is rarer and typically used for teeth or organic matter.

Common Mistakes

My shoes decayed after a year of use.
My shoes wore out after a year of use.
'Decay' is for natural rotting or chemical breakdown, not general wear and tear.
The milk decayed in the fridge.
The milk went bad in the fridge.
For food that becomes unsafe to eat, 'go bad' or 'spoil' are more natural than 'decay'.

2. when a radioactive substance such as uranium or carbon-14 changes naturally into

2.verbintransitiveC1
Definition

when a radioactive substance such as uranium or carbon-14 changes naturally into another substance by releasing radiation from its atoms

Example

Uranium-238 decays into thorium-234 by releasing an alpha particle.

[element] + decays into + [element]

Scientists measure how fast a radioactive material decays to find out how old something is.

Common collocations
  • decay into
  • decay at a rate
  • undergo decay
Synonyms
  • break down

    less technical, describes the process in everyday language

  • disintegrate

    suggests the nucleus breaking apart into smaller pieces

Grammar Patterns

decay + into + noun phrase (resulting element)

Usage Note

Subject is always a radioactive element or isotope. The rate of decay is constant for each substance and cannot be changed by outside conditions.

Common Mistakes

The scientist decayed the uranium in the lab.
The uranium decayed naturally in the lab.
'Decay' for radioactive substances is always intransitive; no one can 'decay' a radioactive element.

decay — noun

Word family

  • decayed
    adjectiveB2
  • decaying
    adjectiveB2
  • decayer
    nounC2
  • decayable
    adjectiveC2
  • decadence
    nounC1
  • decadent
    adjectiveC1

Synonym discussion

Sense: verb/1

'Rot' is the most concrete of these words — it describes organic matter breaking down, usually with a smell ('The fruit rotted in the sun'). 'Decompose' is the scientific term for the same chemical process and is common in biology ('Leaves decompose into soil'). 'Deteriorate' is more formal and can refer to anything that gets worse, from health to roads to skills ('Her eyesight deteriorated with age'). 'Decline' focuses on a loss of quality, strength, or amount, often in gradual stages over a long period ('The company's profits declined for five years'). Of the four, 'decay' sits in the middle — it can be concrete like 'rot' or abstract like 'deteriorate', which makes it more flexible but less specific. For example, you can say 'moral decay' or 'urban decay', but not 'moral rot' or 'urban deterioration' in quite the same way.

rotdeteriorate ↗decompose ↗decline ↗

Common collocations

Nouns

Adverbs

Phrases

  • fall into decay
  • in a state of decay
  • rate of decay
  • signs of decay
  • decay sets in

Prepositions

Etymology

LatinFrenchEnglish

Decay entered English from Old French 'decair' (to fall away, decline), which in turn came from Latin 'dēcadere' — a combination of the prefix 'dē-' (down, away from) and 'cadere' (to fall). The literal sense of 'falling down or away' gradually developed into the modern meaning of 'falling apart or deteriorating through natural processes'.