decay

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. Biology To break down into component parts; rot.
2. v. Physics To disintegrate or diminish by radioactive decay.
3. v. Electronics To decrease gradually in magnitude. Used of voltage or current.
4. v. Aerospace To decrease in orbit. Used of an artificial satellite.
5. v. To fall into ruin: a civilization that had begun to decay.
6. v. Pathology To decline in health or vigor; waste away.
7. v. To decline from a state of normality, excellence, or prosperity; deteriorate.
8. v. To cause to decay.
9. n. The destruction or decomposition of organic matter as a result of bacterial or fungal action; rot.
10. n. Rotted matter.
11. n. Physics Radioactive decay.
12. n. Aerospace The decrease in orbital altitude of an artificial satellite as a result of conditions such as atmospheric drag.
13. n. A gradual deterioration to an inferior state: tooth decay; urban decay.
14. n. A falling into ruin.

Century Dictionary and Cyclopedia

1. To pass gradually from a sound or perfect state to a less perfect state, or toward weakness or dissolution; fall into an inferior condition or state; specifically, become decomposed or corrupted; rot.
2. Synonyms Putrefy, Corrupt, etc. See rot.
3. To cause to become unsound or impaired; cause to deteriorate; impair; bring to a worse state.
4. n. Gradual loss of soundness or perfection; a falling by degrees into an impaired condition or state; impairment in general; loss of strength, health, intellect, etc.
5. n. Specifically Decomposition; putrefaction; rot.
6. n. 3. Death; dissolution.
7. n. . A disease; especially, consumption.
8. n. . A cause of decay.
9. n. Loss of fortune or property; misfortune; ruin : applied to persons.
10. n. . plural Ruins.
11. n. Synonyms Decline, decadence, deterioration, degeneracy, withering.

Wiktionary

1. n. The process or result of being gradually decomposed.
2. n. A deterioration of condition.
3. v. intransitive To deteriorate, to get worse, to lose strength or health, to decline in quality.
4. v. intransitive To rot, to go bad.
5. v. intransitive, transitive, physics, chemistry To change by undergoing fission, by emitting radiation, or by capturing or losing one or more electrons.
6. v. intransitive, transitive, physics To undergo optical decay, that is, to relax to a less excited state, usually by emitting a photon or phonon.
7. v. transitive To cause to rot or deteriorate.

GNU Webster's 1913

1. v. To pass gradually from a sound, prosperous, or perfect state, to one of imperfection, adversity, or dissolution; to waste away; to decline; to fail; to become weak, corrupt, or disintegrated; to rot; to perish
2. v. rare To cause to decay; to impair.
3. v. obsolete To destroy.
4. n. Gradual failure of health, strength, soundness, prosperity, or of any species of excellence or perfection; tendency toward dissolution or extinction; corruption; rottenness; decline; deterioration.
5. n. obsolete Destruction; death.
6. n. rare Cause of decay.

WordNet 3.0

1. n. the process of gradually becoming inferior
2. n. a gradual decrease; as of stored charge or current
3. n. the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation
4. v. undergo decay or decomposition
5. v. lose a stored charge, magnetic flux, or current
6. v. fall into decay or ruin
7. n. the organic phenomenon of rotting
8. n. an inferior state resulting from the process of decaying