Third-person singular simple present indicative form of let bygones be bygones

(idiomatic) To disclose a secret; to let a secret be known, often inadvertently.

(idiomatic) To leave things as they are; especially, to avoid restarting or rekindling an old argument; to leave disagreements in the past.

(idiomatic) To relax and enjoy oneself.

(chiefly imperative) To have fun or live fully; may imply letting things that are going well proceed; if it ain't broke, don't fix it.

(colloquial, humorous) Used to wish a person a good night's sleep.

Third-person singular simple present indicative form of let one's hair down

present participle of let one's hair down

(idiomatic) To insist on the total realization of a goal and reject any compromise, thereby decreasing the chance of achieving even a part of that goal.

Get out of the way, so I can see what I'm doing.