lifeline
noun [ C ] uk/ˈlaɪf.laɪn/ us/ˈlaɪf.laɪn/
命脉，生命线
something, especially a way of getting help, that you depend on to lead your life in a satisfactory way
For many old people living on their own the phone is their lifeline to the outside world. 对很多独居的老人而言，电话是他们与外界联系的生命线。
（尤指海上救援的）救生索
a rope that is thrown to someone who is in the water, especially the sea, and is in danger