back up

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back up (third-person singular simple present backs up, present participle backing up, simple past and past participle backed up)

1. (idiomatic, intransitive) To move backwards, especially for a vehicle to do so.

   That beeping sound indicates that the truck is backing up.

2. (idiomatic, transitive) To move a vehicle backwards.

   Back up the car a little, you're blocking the driveway.

   • 1898, Winston Churchill, chapter 5, in The Celebrity:

     We expressed our readiness, and in ten minutes were in the station wagon, rolling rapidly down the long drive, for it was then after nine. […] As we reached the lodge we heard the whistle, and we backed up against one side of the platform as the train pulled up at the other.

3. (idiomatic, intransitive) To undo one's actions.

   I couldn't see how to finish the project, so I backed up and tried it another way.

4. (idiomatic, intransitive) To reconsider one's thoughts.

   This isn't working. Let's back up and think about it.

5. (idiomatic, computing, transitive) To copy (data) so that it can be restored if the main copy is lost.

   Back up your documents folder before applying the update.

6. (idiomatic, transitive) To provide support or the promise of support to.

   You should be careful. This guy is backed up by the local gang.

   When he said I wasn't there, I told him I was, and my buddy backed me up.

7. (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.
8. (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.
9. (idiomatic, intransitive, of a blockage) To halt the flow or movement of something.

   When I flushed the toilet, the plumbing backed up and burst.

10. (idiomatic, intransitive, informal) To fill up because of a backlog.
    • 1995, "Oubliette" (episode of The X-Files TV series)

      WAITRESS: Hurry up with those drinks, Lucy. We're backing up. (Grabs the drinks LUCY has poured.) What are you doing? These are regular. They all ordered large.

• backupable

• back down
• back into
• back off
• back out

• upback