back up meaning

  "back up" in a sentence
1. back up sthback sth up to prove that something is true:
There was no scientific evidence to back up their claims.
It was fortunate that the videotape backed up the manager's story.
SIMILAR TO: support
2. back sb upback up sb to support someone by saying that they are telling the truth:
Peggy was there too. She'll be able to back me up.
He swears he's telling the truth and has witnesses who will back him up.
3. back up sb/sthback sb/sth up to provide help or support for someone or something:
Officials discussed the possibility of using military forces to back up the police.
a series of security arrangements which would back up a peace deal
solar power, backed up by a propane generator
back-up n singular, U help or support for someone or something:
Several police cars provided back-up for the officers.
back-up adj always before noun back-up systems, services, or equipment are designed to be used if the main one does not work effectively:
Nuclear reactors have superbly efficient back-up systems in case of emergencies.
4. back up sthback sth up to make a copy of information on a computer, and store it on a separate disk or tape so that the information is safe if there is a problem with the computer:
You should back up your data at least once a week.
back-up n C a copy of information on a computer:
The tape drive does an automatic back-up every lunchtime.
Remember to keep back-ups of all your important files.
back-up adj always before noun used or produced when you make a copy of information on a computer:
back-up disks
a back-up copy
5. back upback up sthback sth up if you back up or back a vehicle up, you drive backwards:
Will you back up a bit so that I can get through, please?
The driver backed the taxi up to the hotel door.
SIMILAR TO: reverse BrE
6. back up if traffic backs up, it stops moving and forms a long line because there are so many vehicles:
If you leave town after five o'clock the traffic starts backing up really badly.

[American idiom]
to support someone or something; to concur with someone.
Please back me up in this argument.
I would like you to back up John in this discussion.

[American slang]
to go back to something said in a conversation.
  Wait—back up a little. What did you say that phone number was?
  Let's back up to what you just said and go over that point again.

(1) When bond yields rise and prices fall, the market is said to backup. (2) An investor who swaps out of one security into another of shorter current maturity is said to back up.


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  1. his offhand manner put my back up.
  2. to back up tiles is tedious work.
  3. do you have any facts to back up all this?
  4. prissy edged back up the stairs.
  5. note that we back up over ignored characters too.

Related Words

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PC Version