Did you know?

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

extension - 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.

noun     extension pronunciation in British English
Word Forms
  1. 1
    [countable] an extra room or rooms added to a building

    We are building an extension on the back of our house.

    extension to:

    He has applied for permission to build a single-storey extension to his house.

  2. 2
    [countable] a telephone line that is one of several lines coming from a main line

    What’s your extension?

    I’m on extension 334.

    a new extension number

  3. 3
    [countable] extra time that you are given to finish a piece of work, especially at college or university
    extension on:

    I’m going to ask for an extension on this essay.

    1. a.
      extra time that you are given to pay money that you owe
      extension on:

      Will the bank give you an extension on the loan?

    2. b.
      extra time that you are given to use a particular legal document or right

      a visa extension

      extension to:

      Brady wants a two-year extension to his contract.

    3. c.
      extra time that a shop, business, or bar is allowed to stay open

      There was a bar extension until midnight.

      extension to:

      Local shops have been granted an extension to opening hours.

  4. 4
    [countable] something that you add to a long thin object to make it able to reach somewhere

    This lead isn’t long enough – do you have an extension?

    1. a.


      [plural] long pieces of artificial hair that can be fastened to someone’s hair to make it look longer
  5. 5
    [countable] something that develops from a particular custom, activity, idea etc
    extension of:

    Business entertainment seems a natural extension of Japan’s gift-giving culture.

    He sees local history as an extension of family history.

  6. 6
    [uncountable] formal the action of stretching part of your body

    His leg was now capable of full extension.

  7. 7
    [singular/uncountable] an increase in the power of something
    extension of:

    the further extension of state control

  8. 8
    [countable] computing the last part of the name of a computer file. For example, ‘exe’ and ‘doc’ are extensions.
  9. 9
    [uncountable] in the UK, a system in which students can take courses at a university without being full-time students

    courses provided through university extension

  • 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