extension

ex|ten|sion /ɪkst'enʃ^ən/ (extensions)
1 [N-COUNT]
An extension is a new room or building which is added to an existing building or group of buildings.
2 [N-COUNT] usu with supp
An extension is a new section of a road or rail line that is added to an existing road or line.
...the Jubilee Line extension.
3 [N-COUNT]
An extension is an extra period of time for which something lasts or is valid, usually as a result of official permission.
He first entered Britain on a six-month visa, and was given a further extension of six months...
4 [N-COUNT] usu N of n
Something that is an extension of something else is a development of it that includes or affects more people, things, or activities.
Many Filipinos see the bases as an extension of American colonial rule...
5 [N-COUNT] also N num
An extension is a telephone line that is connected to the switchboard of a company or institution, and that has its own number. The written abbreviation ext. is also used.
She can get me on extension 308...
6 [N-COUNT]
An extension is a part which is connected to a piece of equipment in order to make it reach something further away.
...a 30-foot extension cord...