Definition of: decay

(di·kā′) v.i.
1. To fail slowly in health, beauty, quality, or any form of excellence.
2. To rot; decompose.
—v.t.
3. To cause to decay.
—noun
1. A passing into a feeble or reduced condition tending toward dissolution.
2. A gradual decline in health, size or quality; deterioration.
3. Decomposition; corruption; rottenness.
4. Physics The disintegration of a radioactive element. See synonyms under RUIN. [<OF decair, var. of decaoir <L decidere < de- down + cadere fall]
—de·cay′·a·ble adjective
—de·cay·ed·ness (di·kā′id·nis) noun Synonyms (verb): corrupt, decompose, molder, putrefy, rot, spoil. Rot is a strong and direct word. To say that a thing is decayed may denote only a partial result, but to say it is decomposed ordinarily implies that the change is complete or nearly so. Putrefy and the adjectives putrid and putrescent, and the nouns putridity and putrescence, are used almost exclusively of animal matter in a state of decomposition, the more general word decay being used of either animal or vegetable substances. Decay may also be extended to any process of decline or breaking down, physical, mental, social, etc. See PUTREFY.