vi.

1. 腐朽，腐烂；蛀蚀
   Sweet potatoes decayed after the frost.

   霜下了之后，红薯烂掉了。

2. 衰败；衰退
   The Turkish Empire decayed in the nineteenth century.

   土耳其帝国在十九世纪时衰落。

vt.

1. 使腐朽，使腐烂
2. 使（牙齿）蛀坏
   Sweets can decay the teeth.

   糖果会蛀蚀牙齿。

n.[U]

1. 腐朽，腐烂；蛀牙
   They are figuring out a way to stop the decay of the ancient building.

   他们在想办法阻止这古老建筑的朽坏。

2. 衰败；衰退
   His mental decay is distressing.

   他的智力衰退令人苦恼。

3. （放射性物质的）蜕变
4. 人造卫星重返大气层的日期

v.

1. rot or cause to rot through the action of bacteria and fungi; decompose.
   ▸decline in quality or vigour; deteriorate.
2. Physics  (of a radioactive substance, particle, etc.) undergo change to a different form by emitting radiation.

n.

1. the state or process of decaying.
2. rotten matter or tissue.