Definition of extension noun from the Oxford Advanced American Dictionary

      

    extension

     noun
    noun
    NAmE//ɪkˈstɛnʃn//
     
     
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    increasing influence
  1. 1[uncountable, countable] extension (of something) the act of increasing the area of activity, group of people, etc. that is affected by something the extension of new technology into developing countries a gradual extension of the powers of central government The bank plans various extensions to its credit facilities. My home life was becoming no more than an extension of my job.
  2. extra time
  3. 2 [countable] extension (of something) an extra period of time allowed for something He's been granted an extension of the contract for another year. a visa extension She was given an extension to finish writing her thesis.
  4. telephone
  5. 3[countable] (abbreviation ext.) an extra telephone line connected to a central telephone in a house or to a switchboard in a large building. In a large building, each extension usually has its own number We have an extension in the bedroom. What's your extension number? Can I have extension 4332 please?
  6. making something longer/larger
  7. 4 [uncountable, countable] the act of making something longer or larger; the thing that is made longer and larger The extension of the subway will take several months. extensions to the original railroad track hair extensions (= pieces of artificial hair that are added to your hair to make it longer)
  8. of building
  9. 5 [countable] a new room or rooms that are added to a house
  10. college/university
  11. 6 [countable] a part of a college or university that offers courses to students who are not studying full-time; a program of study for these students extension courses
  12. computing
  13. 7the set of three letters that are placed after a dot at the end of the name of a file and that show what type of file it is The extension .doc indicates a word-processing file.
  14. Idioms
    by extension(formal)
     
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    taking the argument or situation one stage further The blame lies with the teachers and, by extension, with the Board of Education.
See the Oxford Advanced Learner's Dictionary entry: extension