decay

From Middle English decayen, dekeyen (“to decrease, diminish”), from Anglo-Norman decäir (“to fall away, decay, decline”), from Medieval Latin *dēcadere, restored form of Latin decidere (“to fall away, fail, sink, perish”), from de (“down”) + cadere (“to fall”); compare decadent and decadence.

• (UK) IPA^(key): /dɪˈkeɪ/
• Rhymes: -eɪ
• (US) enPR: dē-kāʹ, IPA^(key): /di.ˈkeɪ/

decay (countable and uncountable, plural decays)

1. The process or result of being gradually decomposed.
   • 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 or fortune.

decay (third-person singular simple present 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.
   • 2005, Encyclopedia of Earth Science (edited by Timothy M. Kusky; →ISBN, 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.

   • Shakespeare

     Infirmity, that decays the wise.

• decay in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.
• decay in The Century Dictionary, New York, N.Y.: The Century Co., 1911.

• Dacey