Definitions from Wiktionary (back up)

▸ verb:  (idiomatic, intransitive) To move backwards, especially for a vehicle to do so.
▸ verb:  (idiomatic, transitive) To move a vehicle backwards.
▸ verb:  (idiomatic, intransitive) To undo one's actions.
▸ verb:  (idiomatic, intransitive) To reconsider one's thoughts.
▸ verb:  (idiomatic, computing, transitive) To copy (data) so that it can be restored if the main copy is lost.
▸ verb:  (idiomatic, transitive) To provide support or the promise of support to.
▸ verb:  (idiomatic, intransitive, cricket) For the non-striker to take a few steps down the pitch, in preparation to taking a run, just as the bowler bowls the ball.
▸ verb:  (idiomatic, intransitive, cricket) For a fielder to position himself behind the wicket (relative to a team-mate who is throwing the ball at the wicket) so as to stop the ball, and prevent overthrows.
▸ verb:  (idiomatic, intransitive, of a blockage) To halt the flow or movement of something.
▸ verb:  (idiomatic, intransitive, informal) To fill up because of a backlog.
▸ verb:  (obsolete, printing) To run a printing press in reverse.

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