olemus
kontekstist sõltuv füüsiline või metafoorne päästevahend

Wiktionary:
1. a line to which a drowning or falling victim may cling
(by extension) A source of salvation in a crisis
5. (nautical) on the deck of a boat, a line to which one can attach oneself to stay aboard on rough seas
6. (underwater diving) a line from the diver to a tender at the surface control point

ülevaateid
https://en.wikipedia.org/wiki/Lifeline_(safety)