Did you know?

Click any word in a definition or example to find the entry for that word

back up - definition and synonyms

What are red words?

90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.

Thesaurus diagram

The thesaurus of synonyms and related words is fully integrated into the dictionary. Click on the thesaurus category heading under the button in an entry to see the synonyms and related words for that meaning.

phrasal verb
Word Forms
present tense
I/you/we/theyback up
he/she/itbacks up
present participlebacking up
past tensebacked up
past participlebacked up
  1. 1
    [transitive] back someone up to give support to someone by telling other people that you agree with them

    If I ask for more money will you back me up?

  2. 2
    [transitive] to show that an explanation or belief is probably true

    All the evidence backs up her story.

  3. 3
    [intransitive/transitive] to make a copy of information on your computer
  4. 4
    [intransitive/transitive] if traffic backs up, or if it is backed up, the vehicles are in a long line and waiting to continue moving

    Cars were backed up for miles.

    1. a.
      if a toilet, sink, or drain backs up, or if it is backed up, water cannot flow through it because something is blocking it
    2. b.
      if a system backs up, or if it is backed up, it has slowed down or stopped working because there is too much of something for it to deal with

      Orders are really backed up this month.

  5. 5
    [intransitive] to move backwards a short distance

    I need everyone to back up about 10 paces.

  6. 6
    [intransitive/transitive] to make a car go backwards

    See if you can back up a bit further.

    back something up something:

    I’ll back the car up the driveway.

  7. 7
    [intransitive] mainly American used for telling someone to return to something that was said earlier

    Back up: didn’t you say they had already met?

See also main entry: back
  • Facebook
  • Twitter


a lifestyle focussing on simple pleasures such as comfort and cosiness in the home, and spending time with friends and family

BuzzWord Article

Open Dictionary


a form of location that involves the underwater detonation of a bomb which causes sound waves that are picked up by ships

add a word


A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

global English and language change from our blog
Macmillan learn live love play