# decay

Pronunciation: US say "dee-KAY" /diˈkeɪ/; UK say "di-KAY" /dɪˈkeɪ/

## Verb

1. Of plant or animal matter, to rot or go bad.
   - Simple: To rot or go bad, as food, plants and dead animals do.
   - _Without refrigeration, the fish decayed within a day._
   - _Fallen logs decay slowly in cold northern forests._
3. To deteriorate or decline, losing strength, health or quality.
   - Simple: To get worse, weaker or less healthy over time.
   - _Tourists photograph the decaying mansions along the waterfront._
   - _Standards at the paper decay a little more with every round of layoffs._
5. To cause something to rot or deteriorate.
   - Simple: To make something rot or get worse.
   - _Salt spray had decayed the pier's wooden pilings._
   - _Years of neglect decay even the strongest institutions._
6. Of an unstable atom, to change by fission, by giving off radiation, or by capturing or losing electrons; to undergo radioactive decay.
   - Simple: Of an unstable atom, to change by splitting, giving off radiation, or gaining or losing electrons.
   - _Carbon-14 atoms decay at a steady rate, which lets scientists date ancient bones._
   - _When the nucleus decayed, it released an alpha particle._
9. Of a satellite's orbit, to lose altitude above the orbited body over a long period.
   - Simple: Of a satellite's path in space, to slowly get lower over a long time.
   - _Low orbits decay faster than high ones because the air is thicker closer to the ground._
   - _Engineers expect the probe's orbit to decay within a decade, ending in a fiery reentry._
11. Of software, to undergo software rot, falling behind a changing environment through lack of updates until it becomes legacy or obsolete.
   - Simple: Of a computer program, to slowly become out of date because nobody updates it while everything around it changes.
   - _Code that no one maintains will decay as the libraries and operating systems around it move on._
   - _The billing system had quietly decayed into legacy software that only one engineer understood._
12. Of storage media or the data stored on them, to degrade gradually through bit rot.
   - Simple: Of a disk or the files on it, to slowly get damaged and lose information over time.
   - _Data on magnetic tape can decay over the decades unless it is copied to fresh media._
   - _Archivists found that several of the floppy disks had decayed beyond recovery._
13. Of a quantum system, to relax into a less excited state, usually by emitting a photon or phonon.
   - Simple: Of an atom or other tiny system, to drop to lower energy, usually giving off light or a vibration.
   - _Excited molecules in the sample decayed to the ground state, each emitting a photon._
   - _In a crystal, an excited state may decay by emitting a phonon rather than light._
14. To lose airspeed because of drag, said of an aircraft or of its speed.
   - Simple: Of a plane or its speed, to slow down because the air pushes against it.
   - _With the engine at idle and the landing gear down, the airspeed decayed quickly._
   - _Pilots must add power on approach or the airspeed will decay below a safe margin._
15. In programming, of an array, to be silently converted into a pointer, losing its type and dimensions, as when it is passed to a function.
   - Simple: In programming, for an array to turn into a simple pointer and lose its size and type.
   - _In C, an array decays to a pointer as soon as it is passed to a function._
   - _Arrays decay silently, so sizeof inside the function reports the size of a pointer instead._

## Noun

2. The gradual process of rotting or decomposing, or the decomposed state that results.
   - Simple: The slow rotting of something, or the rotten part that is left.
   - _Brushing twice a day helps prevent tooth decay._
   - _The hikers smelled the decay before they saw the dead elk._
4. A decline in condition, or a loss of status, quality, strength or fortune.
   - Simple: A loss of quality, strength, importance or wealth.
   - _Critics blamed the scandal on a wider moral decay in public life._
   - _The once-grand hotel had fallen into decay by the 1970s._
7. Ellipsis of radioactive decay. — Ellipsis of radioactive decay.
   - Simple: Short for radioactive decay. Scientists often just say decay.
   - _Alpha decay releases a helium nucleus and leaves behind a lighter element._
   - _Heat from decay deep inside the earth helps keep its interior hot._
8. A gradual decrease in a stored electric charge, a magnetic flux, a current, or a similar quantity.
   - Simple: The slow fading of stored electricity, a magnetic field or an electric current.
   - _Engineers measured the decay of current in the coil after the switch was opened._
   - _Charge decay in the memory cells means the data must be refreshed constantly._
10. The gradual change in the path of a satellite orbiting Earth, caused by drag from the atmosphere.
   - Simple: The slow change in a satellite's path around Earth, caused by air pushing against it.
   - _Atmospheric drag produces a steady decay in the orbits of satellites flying low over Earth._
   - _Mission planners must account for decay when predicting where an old satellite will reenter the atmosphere._
16. In programming languages such as C, the loss of an array's type and dimensions when it is reduced to a pointer, for example by being passed to a function.
   - Simple: In some programming languages, the way an array turns into a simple pointer and loses its size and type.
   - _Many subtle bugs in C code trace back to array decay inside function calls._
   - _Wrapping the array in a struct is one way to prevent decay when passing it around._

## Noun

17. Downfall or destruction; the overthrow or ruin of someone or something. *(obsolete)*
   - Simple: The complete fall or ruin of someone or something.

## Origin

From Middle English decayen ("to decrease, diminish"), from Anglo-Norman decaeir ("to fall away, decay, decline"), from Vulgar Latin *dēcadere, a restored form of Latin dēcidere ("to fall away, fail, sink, perish"), from de ("down") + cadere ("to fall"). Compare decadent and decadence.

Source: DictionaryAI, https://dictionaryai.com/define/decay (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).