lest

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]他唯恐有人认为他有罪。

And lest you think I'm joking, let me assure you that everything I've said is true.为了不让你以为我在开玩笑，我向你保证，我所说的一切都是真的。

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]她是有才华的歌手，还有，别忘了，她也是优秀的音乐家。