decay的基本意思是通过化学变化而“(使)腐烂,(使)腐朽”。可用来比喻因体力、精力、活力或影响力等的丧失而“衰败,衰退,衰落”至一个较原来低或差的状态,此时只用作不及物动词。

用作不及物动词
▲S+～(+A)
The cabbages had already started to decay. 卷心菜已经开始烂了。
They claimed that the plastics wouldn't decay if they were buried. 他们声称塑料被埋起来就不会腐烂。
Facilities built in the 1960s have started to decay. 建于20世纪60年代的设施开始损坏了。
The role of the extended family has been decaying for some time. 大家庭的作用已开始在一段时间内有所减退。
The human world, being what it is, could only decay in the course of time. 人类的世界，就其现状而言，最终非衰败不可。
用作及物动词
▲S+～+n./pron.
Pollution has decayed the surface of the stonework on the front of the cathedral. 污染已腐蚀了教堂前部的石头雕塑。
其他
She smelt the unpleasantly sweet smell of decaying meat. 她闻到了肉类腐烂发出的变质臭味。

［同义词］ v. rot, spoil
［反义词］ v. flourish, grow, progress
［词源］＜古法语decair(烂掉)

The decay of the meat could have been prevented by proper refrigeration.如果经过适当的冷藏，这些肉本来不至于腐烂掉。
The decay had not proceeded very far.腐烂的还不算厉害。
The corpse was preserved from decay by embalming.尸体用香料涂抹以防腐烂。
Dental decay in children in Britain has almost reached epidemic levels. 在英国，儿童蛀牙之普遍几乎达到了流行病的程度。
Neglect has accelerated this house's decay.这栋房子因没有人管理而加快损坏。
That university has fallen into decay in the last 50 years.那所大学在过去的50年逐渐没落了。
The buildings had started to fall into decay. 建筑物开始衰败。
This industry has been in decay for some time. 这一工业进入衰败期已有一段时间。