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English definition of “extension”

extension

noun [C] (PHONE)   /ɪkˈsten·ʃən/ (abbreviation ext.)
any of two or more telephones in the same house that share the same number: We have an extension in our bedroom. An extension is also any of the telephones connected to a central system, esp. in a business.
(Definition of extension noun (PHONE) from the Cambridge Academic Content Dictionary © Cambridge University Press)
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