lest 
/ˈlɛst/ conjunction
/ˈlɛst/ conjunction formal + literary 1 : for fear that — used to say that you do not want something to happen ▪ He was concerned lest anyone think that he was guilty. = (chiefly Brit) He was concerned lest [=in case] anyone should think he was guilty. [=he was concerned that people would think he was guilty; he did not want anyone to think he was guilty] 2 — used when you are saying something in order to prevent something from happening ▪ And lest you think I'm joking, let me assure you that everything I've said is true. ▪ She's a talented singer and, lest we forget, a fine musician as well. [=we should not forget that she is also a fine musician]
