lifeline

noun

1. a line, fired across a ship or boat, by means of which a hawser for a breeches buoy may be hauled aboard.
2. a line or rope for saving life, as one attached to a lifeboat.
3. any of various lines running above the decks, spars, etc., of a ship or boat to give sailors something to grasp when there is danger of falling or being washed away.
4. a wire safety rope supported by stanchions along the edge of the deck of a yacht.
5. the line by which a diver is lowered and raised.
6. any of several anchored lines used by swimmers for support.
7. a route or means of transportation or communication for receiving or delivering food, medicine, or assistance: This road is the town’s lifeline and must be kept open despite the snow.
8. assistance at a critical time.

noun

1. a line thrown or fired aboard a vessel for hauling in a hawser for a breeches buoy
2. any rope or line attached to a vessel or trailed from it for the safety of passengers, crew, swimmers, etc
3. a line by which a deep-sea diver is raised or lowered
4. a vital line of access or communication

n.also life-line, 1700, “rope used somehow to save lives,” from life (n.) + line (n.); figurative sense first attested 1860. Sense in palmistry from 1890.