conj.唯恐,以免,惟恐,生怕
Be careful lest you ( should ) fall from the tree.
小心,不要从树上掉下来.
He gripped his brother's arm lest he be trampled by the mob.
他紧抓着他兄弟的胳膊,怕他让暴民踩着。
They decided to retreat lest they would be between two fires.
他们决定撤退,否则就要受两面夹击.