1 useless; failing to produce the result you want 无用的;徒劳的:
She turned away in a vain attempt to hide her tears.她转过身去,想要掩饰自己的眼泪,可惜白费力气。
2 (used about a person) too proud of your own appearance, abilities, etc (指人)爱虚荣的,自负的,自视过高的:
He's so vain -- he looks in every mirror he passes.他很爱虚荣,每经过一面镜子都要照一照。☞noun vanity 名词为vanity➔vainlyadv
in vain without success 徒然;白费力:
The firemen tried in vain to put out the fire.消防员尝试扑灭那场火,可惜徒劳无功。