lifeline

1. (by extension) A source of salvation in a crisis.Examples: "The girls, of course, were my lifeline during this time."; "Slowly I began to fill up some of the emptiness inside—writing had become my lifeline."; "The Government has thrown a lifeline to Alstom's Derby Works, with an offer of an order for ten Class 345 nine-car electric multiple units (EMUs) for the Elizabeth line - but only if the 'price is right'."broadly

2. (engineering) A system or structure of vital importance to a community.

3. (nautical) On the deck of a boat, a line to which one can attach oneself to stay aboard on rough seas.Synonyms: jackstay

4. (underwater diving) A line from the diver to a tender at the surface control point.Synonyms: tether

5. (palmistry) A particular crease in the palm.Synonyms: line of life