DuckCorp Dico

Found one definition

1.                 From English-日本語 (にほんご) FreeDict+WikDict dictionary ver. 2022.11.18:
                   
   
   
                   
                     
   extension //ɪkˈstɛnʃən// <n>
   1. 伸展, 延長, 拡大, 拡張
   act of extending or the state of being extended
   2. 伸展
   anatomy: that property of a body by which it occupies a portion of space
   3. 延期, 延長, 猶予
   finance: written engagement on the part of a creditor
   4. 牽引
   medicine: operation of stretching a broken bone
   5. 範囲, 限度
   semantics: capacity of a concept or general term to include a greater or smaller number of objects
   6. 内線
   telecommunication: phone extension number
   7. ストレッチ
   weightlifting: an exercise