Definition of "Lifeline" :

noun: line thrown from a vessel that people can cling to in order to save themselves from drowning

noun: line that raises or lowers a deep-sea diver

noun: support that enables people to survive or to continue doing something (often by providing an essential connection)

"The airlift provided a lifeline for Berlin."

noun: a crease on the palm; its length is said by palmists to indicate how long you will live