The manager decided to extend the deadline by two weeks due to the project's smooth progress.

extend 是动词，意思是"延长、扩展"。这个词由前缀 ex-（表示"向外"）和词根 tend（表示"伸展"）组成，字面意思是"向外伸展"，引申为"延长（时间）、扩展（范围）"等含义。