1 an extra period of time that you are allowed for sth 额外期限: I've applied for an extension to my work permit. 我已申请把工作许可证的限期延长。

2 a part that is added to a building （建筑物的）扩建部份: They're building an extension on the hospital. 医院的扩建工程正在进行。

3 a telephone that is connected to a central phone in a house or to a central point (switchboard) in a large office building 电话分机: What's your extension number? 你的分机号码是多少？Can I have extension 4342, please? 请给我接4342分机。