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

decay

1. The process or result of being gradually decomposed.
2. A deterioration of condition; loss of status or fortune.

• deciduous

• French: décrépitude
• German: Verfall, Verwesung
• Portuguese: deterioração, apodrecimento, putrefação, decomposição
• Russian: разложе́ние

• Russian: упа́док

decay (decays, present participle decaying; 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.
   • 2005, Encyclopedia of Earth Science (edited by Timothy M. Kusky; ISBN 0-8160-4973-4, page 349:

     Uranium decays to radium through a long series of steps with a cumulative half-life of 4.4 billion years.

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, William Shakespeare, “Twelfe Night, or VVhat You VVill”, in Mr. William Shakespeares Comedies, Histories, & Tragedies: Published According to the True Originall Copies (First Folio), London: Printed by Isaac Iaggard, and Ed[ward] Blount, published 1623, OCLC 606515358 ↗, [Act I, scene v]:

     Infirmity, that decays the wise.

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

• German: verfaulen, verrotten, verwesen
• Portuguese: apodrecer, estragar, putrefazer
• Russian: разлага́ться
• Spanish: pudrir