in vain 徒劳;白费力气;无用的;无意义的;无价值的

【例句】
They tried in vain to persuade her to go.
他们极力劝说她去，但枉费了一番口舌。

I dare not imagine anything. i am afraid everything would turn out to be in vain.
我不敢去想象，我怕梦醒之后，一切都是虚伪。