vain
单词辨析：
指努力、希望、搜寻等未能获得想要的结果的。
He underwent a knee operation in the vain hope of getting into the team.
他做了膝盖手术，徒劳地指望能进入该队。
She raised her head in a vain attempt to hold back the tears.
她仰起头，却无法忍住眼泪。
指行动、计划等没有成功的。
an abortive takeover bid by the larger firm
由较大公司提出的夭折了的并购
There is no record of the abortive military coup.
没有关于那次未遂的军事政变的记录。
尤指付出很多努力却无成效的。
So far, their research has been fruitless.
到目前为止，他们的研究工作毫无结果。
The fruitless attempt to settle the dispute disappointed him.
试图解决争端的努力白费了，这让他很失望。
侧重指人或事物未能发挥应有之作用的。
The army has proved ineffective in protecting the local civilians.
军队没有起到保护当地平民的作用。
This special stain remover was almost ineffective in removing the soup stain.
这种特效去污剂基本去不掉汤渍。
The policy proved ineffective in dealing with the problem.
事实证明该政策未能解决问题。
相关例句：
Their hopes were but vain.
他们的希望只不过是妄想。
It became obvious that all her complaints were in vain.
很明显她所有的抱怨都是白费口舌。
Isabelle was a frivolous little fool, vain and flighty.
伊莎贝尔是个轻佻、没头脑的小女人，非常虚荣又反复无常。
All efforts of mediation by a third party were in vain at all.
第三方所作的从中调解的一切努力均告失败。
It's no use for you to wait here in vain.
你死耗在这儿没用。
Our efforts were not in vain.
我们没有白忙。