From Middle English decayen, dekeyen, from Anglo-Norman decheoir, from Vulgar Latin , etymologically restored form of Latin dēcidō, from de ("down") + cadere.

• (British) IPA: /dɪˈkeɪ/
• (America) enPR: dē-kāʹ, IPA: /di.ˈkeɪ/

decay

1. The process or result of being gradually decomposed; rot, decomposition.
   • 1895, H. G. Wells, chapter X, in The Time Machine:

     I fancied at first the stuff was paraffin wax, and smashed the jar accordingly. But the odor of camphor was unmistakable. It struck me as singularly odd, that among the universal decay, this volatile substance had chanced to survive, perhaps through many thousand years.

2. A deterioration of condition; loss of status, quality, strength, or fortune.

   civic and moral decay

   systemic decay

3. (obsolete) Overthrow, downfall, destruction, ruin.
   • c. 1587–1588, [Christopher Marlowe], Tamburlaine the Great. […] The First Part […], 2nd edition, part 1, London: […] [R. Robinson for] Richard Iones, […], published 1592, →OCLC ↗; reprinted as Tamburlaine the Great (A Scolar Press Facsimile), Menston, Yorkshire, London: Scolar Press, 1973, →ISBN, Act II, scene vi ↗:

     Let’s cheere our ſouldiers to incounter him,
     That grieuous image of ingratitude:
     That fiery thirſter after Soueraigntie: […]
     Reſolue my Lords and louing ſouldiers now,
     To ſaue your king and country from decay:

4. (programming) The situation, in programming languages such as C, where an array loses its type and dimensions and is reduced to a pointer, for example by passing it to a function.

• deciduous

• French: décrépitude
• German: Verfall, Verwesung, Fäulnis
• Portuguese: deterioração, apodrecimento, putrefação, decomposição
• Russian: разложе́ние
• Spanish: descomposición, deterioración, putrefacción, podredumbre

• Russian: упа́док
• Spanish: deterioración, desintegración, decadencia

decay (decays, present participle decaying; simple past and past participle decayed)

1. (intransitive) To deteriorate, to get worse, to lose strength or health, to decline in quality.

   The pair loved to take pictures in the decaying hospital on forty-third street.

   1. (intransitive, electronics, of storage media or the data on them) To undergo bit rot, that is, gradual degradation.
   2. (intransitive, computing, of software) To undergo software rot, that is, to fail to be updated in a changing environment, so as to eventually become legacy or obsolete.
   3. (intransitive, physics, of a satellite's orbit) To undergo prolonged reduction in altitude (above the orbited body).
      • 2009, Francis Lyall, Paul B. Larsen, Space Law: A Treatise, page 120:

        Damaged on lift-off, Skylab was left in orbit until its orbit decayed.

2. (intransitive, of organic material) To rot, to go bad.

   The cat's body decayed rapidly.

3. (intransitive, transitive, physics, chemistry, of an unstable atom) To change by undergoing fission, by emitting radiation, or by capturing or losing one or more electrons; to undergo radioactive decay.
4. (intransitive, transitive, physics, of a quantum system) To undergo optical decay, that is, to relax to a less excited state, usually by emitting a photon or phonon.
5. (intransitive, aviation) Loss of airspeed due to drag.
6. (transitive) To cause to rot or deteriorate.

   The extreme humidity decayed the wooden sculptures in the museum's collection in a matter of years.

   • c. 1601–1602 (date written), William Shakespeare, “Twelfe Night, or What You Will”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC ↗, [Act I, scene v]:

     Infirmity, that decays the wise.

7. (programming, intransitive) Of an array: to lose its type and dimensions and be reduced to a pointer, for example when passed to a function.

• French: pourrir
• German: verfallen, verderben
• Portuguese: decompor-se, deteriorar
• Russian: по́ртиться
• Spanish: deteriorar

• French: se désintégrer
• Russian: распада́ться