the process of making a road, building etc bigger or longer, or the part that is added
making something bigger or longer[uncountable and countable]
the extension of the Jubilee underground line
another room or rooms which are added to a building
extra rooms[countable] British EnglishTBB
the planned extension to the National Museum
a loft extension
an additional period of time allowed for something:
extra time[countable usually singular]
Donald's been given an extension to finish his thesis.
The pub's got an extension tonight (=it will stay open longer than usual).
the development of something in order to make it affect more people, situations, areas than before
include/affect more than before[singular, uncountable]
the extension of the copyright laws to cover online materials
an extension of the powers of the European Parliament
one of many telephone lines connected to a central system in a large building, which all have different numbers:
Can I have extension 316, please?
Do you know Mr Brown's extension number?
one of the telephones in a house that all have the same number
used when you want to mention something that is naturally related to something else:
My primary responsibility is to the pupils, and by extension to the teachers and parents.
long pieces of artificial hair that can be attached to your hair to make it look longer
a set of three letters that follow the name of a computer file to show what it is. For example, the extension '.doc' shows that a file is a written document.
an extension lead
electric wire[countable] British English
the position of a part of the body when it is stretched, or the process of stretching it
stretch arm/leg[uncountable and countable]
part of a university or college that offers courses to people who are not full time students