the process of gradually becoming inferior
"The once-proud city has fallen into decay as its infrastructure crumbles and public services vanish."
the organic phenomenon of rotting
"The rotten wood in the old fence began to decay due to constant exposure to rain and insects."
an inferior state resulting from the process of decaying
"the corpse was in an advanced state of decay"
"the house had fallen into a serious state of decay and disrepair"
the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation
"The scientist monitored the decay of uranium-238 to measure the rate at which it emitted alpha particles."
The process or result of being gradually decomposed.
"The ancient wooden bridge began to decay after years of exposure to rain and dampness."
In plain English: Decay is something that breaks down and rots over time until it falls apart completely.
"The old wood showed signs of decay after being left in the rain for too long."
lose a stored charge, magnetic flux, or current
"the particles disintegrated during the nuclear fission process"
To deteriorate, to get worse, to lose strength or health, to decline in quality.
"The old building began to decay after years of neglect and lack of maintenance."
To undergo bit rot, that is, gradual degradation.
"The digital archive began to decay as bits flipped randomly over time, corrupting the stored images."
In plain English: To decay means to rot, break down, or become ruined over time.
"The old wooden fence began to decay after years of exposure to rain and wind."
Usage: Use decay as a verb when describing the physical breakdown of organic matter or the metaphorical decline of systems and morals over time. It often implies an irreversible loss of strength or quality rather than a temporary setback.
The word decay comes from the Vulgar Latin *dēcadere, meaning "to fall away" or "perish." It entered English via Anglo-Norman and Middle French to describe a decline in value or condition rather than just falling physically.