decline/ dɪ'klaɪn /

1.noun
a decline in sth 某物的下降

2.vt.[+invitation] [ offer] 
(turn down) 谢绝

3.vi.[strength] [ health+] 
衰退

4.vi.[business] [ population+] 
萎缩

to be on the decline/in decline
正在衰落
to fall into decline
衰弱
to decline to do sth
婉言拒绝做某事