A rope or cable that keeps someone safe from falling, or something essential that helps someone survive or stay connected.
Compound of 'life' and 'line'; literally a rope for saving lives. The metaphorical meaning developed in the 1800s for anything vital to survival.
In palm reading traditions, people believed the 'lifeline' on your hand predicted your lifespan—though scientists say it's just random creases, the metaphor stuck because ropes literally save lives!
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