Something that rescues one from difficulties.
A buoyant object (most commonly torus-shaped) that is used as a life-saving device by keeping a person afloat.
A person who saves someone, rescues another from harm.
A child who is born to provide an organ or cell transplant to a sibling who has an otherwise fatal disease (used in combination, with "sibling", "baby", "child", "brother", "sister", etc.)