(transitive, idiomatic) To know (something or someone) very thoroughly.

(intransitive, informal) to fall fast asleep; to sleep soundly / (intransitive, informal) to stop functioning / (intransitive, informal) to die

(Northern England, especially Manchester, Liverpudlian) One's sibling.

(computing) To exit a user account in a computer system, so that one is not recognized until signing in again.

(slang, intransitive) To become extremely emotional or excitable; to lose control of one's emotions. / (slang, transitive) To cause to become extremely emotional or excitable

(slang) A chaotic or crazy episode.

(idiomatic) Of exceptionally high quality; wonderful; marvelous.

(idiomatic) A rift between people or groups, often following a disagreement or quarrel

present participle of fall out

(idiomatic) Used as an intensifier.