extension
nounUK /ɪkˈstenʃn/
US /ɪkˈstenʃn/
An extension is something added to make a thing longer or bigger.
We built an extension on our house so we would have more room.
OTHER MEANINGS
2. Extra time allowed to finish something.
The teacher gave us an extension on our homework.
3. A telephone line connected to the main phone system.
Please call me on extension 204.
4. The act of stretching out a body part.
He raised his arm in extension to reach the top shelf.
5. A set of letters added to the end of a computer file name.
The file has a .jpg extension.