原指已經做完或做過的事，就不必再責怪了。現指對以往的過錯不再責備。

Forgive someone for something he or she did in the past. Allow the unpleasant things that have happened in the past to be forgotten.

Jane: Why don’t you want to invite Ellen to your party?

Frank: She was rude to me at the off ice picnic.

Jane: But that was six months ago. Nancy held a grudge against her teacher for a long time, but she finally decided to let bygones be bygones.