lifeline

Short definition from Wiktionary

Noun

1. 1
   A line to which a drowning or falling victim may cling.
2. 2
   A source of salvation in a crisis.
3. 3
   A means or route for transporting indispensable supplies.
4. 4
   A system or structure of vital importance to a community.
5. 5
   On the deck of a boat, a line to which one can attach oneself to stay aboard on rough seas.
6. 6
   A line from the diver to a tender at the surface control point.
7. 7
   A particular crease in the palm.