As a Noun: 1. A new room or building which is added to an existing building. English = extension. 2. An increase in the size of something created by moving a boundary marking, fence or wall. English = extension. 3. An increase in the amount of time in which some activity is to be completed, made by moving the deadline further into the future. English = extension. 4. Something which is added to a space, building or period of time. English = addition. As a Verb or Adjective: 1. To add a new room or building to an existing building. English = extend. 2. To make something longer or bigger, especially by moving a boundary marking, fence or wall. English = extend. 3. To allow more time in which some activity is to be completed; to give an extension; to give additional time. 4. To be something which is added on to a space, building or period of time. English = (be) additional, (be) extra.