Decay, v. i. [imp. & p. p. Decayed; p. pr. & vb. n. Decaying.]
Etymology: [OF. decaeir, dechaer, decheoir, F. déchoir, to decline, fall, become less; L. de- + cadere to fall. See Chance.]
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; as, a tree decays; fortunes decay; hopes decay. Ill fares the land, to hastening ills a prey, Where wealth accumulates and men decay. Goldsmith.
2 other Webster entries under this spelling
Decay, v. t.
1. To cause to decay; to impair. [R.] Infirmity, that decays the wise. Shak.
2. To destroy. [Obs.] Shak.
Decay, n.
1. Gradual failure of health, strength, soundness, prosperity, or of any species of excellence or perfection; tendency toward dissolution or extinction; corruption; rottenness; decline; deterioration; as, the decay of the body; the decay of virtue; the decay of the Roman empire; a castle in decay. Perhaps my God, though he be far before, May turn, and take me by the hand, and more -May strengthen my decays. Herbert. His [Johnson's] failure was not to be ascribed to intellectual decay. Macaulay. Which has caused the decay of the consonants to follow somewhat different laws. James Byrne.
2. Destruction; death. [Obs.] Spenser.
3. Cause of decay. [R.] He that plots to be the only figure among ciphers, is the decay of the whole age. Bacon.
Syn. -- Decline; consumption. See Decline.
Shades of meaning
Rot is a strong word, ordinarily esteemed coarse, but on occasion capable of approved emphatic use; as, "the name of the wicked shall rot," Prov. x, 7; decay and decompose are now common euphemisms. A substance is decomposed when resolved into its original elements by any process; it is decayed when resolved into its original elements by natural processes; it decays gradually, but may be instantly decomposed, as water into oxygen and hydrogen; 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.