From The Collaborative International Dictionary of English v.0.48:
Decay \De*cay"\, v. i. [imp. & p. p. Decayed; p. pr. & vb. n.
Decaying.] [OF. decaeir, dechaer, decheoir, F. d['e]choir,
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.
[1913 Webster]
Ill fares the land, to hastening ills a prey,
Where wealth accumulates and men decay. --Goldsmith.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Decayed \De*cayed"\, a.
Fallen, as to physical or social condition; affected with
decay; rotten; as, decayed vegetation or vegetables; a
decayed fortune or gentleman. -- De*cay"ed*ness, n.
[1913 Webster]