decay

noun

1. (uncountable, usually)Rot; any processes or result of organic matter being gradually decomposed, especially by microbial action.

   “tooth decay/dental decay—wood-decay fungi—bacterial decay—photochemical decay”

   “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.”

   “He spent himself, the labour of his axe, And leave it there far from a useful fireplace To warm the frozen swamp as best it could With the slow smokeless burning of decay.”

2. (uncountable, usually)Deterioration of condition; loss of status, quality, strength, or fortune.

   “civic and moral decay—systemic decay—fall into decay—urban decay—arrested decay—memory decay”

   “Although the best room of the inn, it had the melancholy aspect of grandeur in decay, and was much too vast for comfort.”

3. (uncountable, usually)Radioactive decay; decomposition of an atom or its nucleus.

   “alpha decay—gamma decay—fission decay—decay chain”

4. (uncountable, usually)Particle decay; decomposition of a sub-atomic particle.
5. (uncountable, usually)Continuous decrease of a quantity.

   “exponential decay—decay rate—orbital decay—decay time—decay constant—time decay”

6. (obsolete, uncountable, usually)Overthrow, destruction, ruin, death.

   “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:”

7. (uncountable, usually)Array decay.

verb

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.”

   “"The signalling at Salisbury has be replaced for safety reasons in the next handful of years. It's worn out. Last week, there was a signal cable issue near Tisbury that stopped proper running for four whole days. The system is decaying.”

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

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

5. (intransitive)To rot, to go bad.

   “The cat's body decayed rapidly.”

   “The largest tree known to us is at Syon (Plate 124), which in 1904 was no less than 60 feet in height by 7 feet in girth and still a fine tree, though its trunk is decaying inside.”

6. (intransitive, transitive)To change by undergoing fission, by emitting radiation, or by capturing or losing one or more electrons; to undergo radioactive decay.

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

7. (intransitive, transitive)To undergo optical decay, that is, to relax to a less excited state, usually by emitting a photon or phonon.
8. (intransitive)Loss of airspeed due to drag.
9. (transitive)To cause to rot or deteriorate.

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

   “Infirmity, that decays the wise.”

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