Merriam-Webster's Collegiate® Dictionary, 11th Edition
DECAY
I. verb see: chance
Date: 15th century
intransitive verb to decline from a sound or prosperous condition, to decrease usually gradually in size, quantity, activity, or force, to fall into ruin, to decline in health, strength, or vigor, to undergo decomposition , transitive verb to cause to decay ; impair , to destroy by decomposition, decayer noun Synonyms: see: decay
II. noun
Date: 15th century
gradual decline in strength, soundness, or prosperity or in degree of excellence or perfection, a wasting or wearing away ; ruin , destruction , death ,
4. rot , the product of decay, a decline in health or vigor, decrease in quantity, activity, or force: as, spontaneous decrease in the number of radioactive atoms in radioactive material, spontaneous disintegration (as of an atom or a particle)