back up

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb to move in a reverse direction; -- used of vehicles or animals.
• intransitive verb to accumulate due to a blockage of flow.
• transitive verb to serve as a backup{3} for (another person or persons).
• transitive verb (Computers) to make a backup{5} of.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• 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) as a security measure.
• verb idiomatic, transitive To provide support or the promise of support.
• 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 to halt the flow or movement of something.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb give moral or psychological support, aid, or courage to
• verb move backwards from a certain position
• verb make a copy of (a computer file) especially for storage in another place as a security copy
• verb establish as valid or genuine
• verb become or cause to become obstructed