(idiomatic, colloquial, usually sarcastic, dismissive) Indicates that the speaker does not agree with a proposed action, and does not wish to participate.

(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.

One should not interfere with promising developments in their early stages.

(idiomatic) To reject or refuse someone in a way that avoids causing hurt or disappointment.

Alternative form of let sleeping dogs lie