Definitions 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)

  Example: "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