lifeboat; rescue boat
Literal meaning: a boat used to rescue people at sea or in emergencies. Often used in historical or dramatic contexts.
When the ship was about to sink in the storm, a nearby fisherman sent out a rescue boat.
helping hand; timely assistance; lifesaver
Figurative use: a person or thing that provides crucial help in a difficult situation, like a lifeboat. Often used in the phrase 助け舟を出す (to throw a lifeline).
When I was struggling with work, my senior colleague threw me a lifeline.
His advice was truly a lifesaver.