v. & n.
--v.
1. a intr. rot, decompose. b tr. cause to rot or decompose.
2 intr. & tr. decline or cause to decline in quality, power, wealth, energy, beauty, etc.
3 intr. Physics a (usu. foll. by to) (of a substance etc.) undergo change by radioactivity. b undergo a gradual decrease in magnitude of a physical quantity.
--n.
1. a rotten or ruinous state; a process of wasting away.
2 decline in health, quality, etc.
3 Physics a change into another substance etc. by radioactivity. b a decrease in the magnitude of a physical quantity, esp. the intensity of radiation or amplitude of oscillation.
4 decayed tissue.
Derivatives:
decayable adj.
Etymology: ME f. OF decair f. Rmc (as DE-, L cadere fall)