英汉词典

1. 唯恐；免得
    If you do something lest something unpleasant should happen, you do it to try to prevent the unpleasant thing from happening.

lest在线翻译

    e.g. I was afraid to open the door lest he should follow me...
           我不敢开门，唯恐他还跟着我。
    e.g. The president has gone along with the hardliners lest they be tempted to oust him...
           总统同意了强硬派的意见，以免他们产生赶他下台的念头。