枉费的英文：
try in vain; waste

参考例句：

He doesn’t want me to bother with American art
他不要我在美国艺术上枉费精神。

It was no use, he could not break away, so he gave up.
这是枉费力气，他挣脱不了，所以只好作罢。

He's flogging a dead horse in trying to persuade people to use canals instead of roads.
他拼命地劝人不要使用公路而去使用运河，真是枉费口舌。

try是什么意思：
v. 尝试，试验，试图，努力；审判；考验
n. 尝试，努力；试验

If at first you don't succeed, try, try again.
初试不成功，努力勿懈怠。

She is trying to slim.
她正在设法减肥。

They are trying to flog their house.
他们正试图卖掉房子。

vain是什么意思：
adj. 空虚的；无价值的；徒劳的；无效的；自负的；爱虚荣的

It was a vain effort.
这种努力是徒劳无益的。

This is a vain and fleeting thing.
这是一种空虚的、转瞬即逝的东西。

She is vain and extravagant.
她既爱虚荣又奢侈。

waste是什么意思：
v. 浪费，滥用，消耗
n. 浪费，废（弃）物，废料，排泄物
adj. 废弃的，无用的

It would be a grievous waste.
那将是一种严重的浪费。

This opportunity is too good to waste.
这个机遇千载难逢，绝不能错过。

"Waste not, want not "
俭则不匮