bygone 名词；let bygones be bygones （尤指既往不咎）过去的事就让它过去吧。
= used to tell someone that they should forget about unpleasant things that happened in the past, and especially to forgive and forget something bad that someone has done to them
扩展 bygone adj.过去的，以往的。= belonging to or happening in a past time 如a bygone era 过去的时代。

【例句】
Just let bygones be bygones and be friends again.
过去的事就别再提了，重归于好吧。

What has happened shall be buried in oblivion.
既往不咎。