lifesaver

noun5

1. •
   Someone or something that saves lives.
2. •
   (figurative) Someone or something that is very useful or helpful.

   • Thank you so much for fixing my car; you're a real lifesaver!
   • This shop is a lifesaver on a hot day when you're craving a cold drink.
3. •
   A lifeguard or other rescuer.

   • My dad loves his job as a surf lifesaver.
   • Paramedics are not just ordinary workers but lifesavers with a very important job.
4. •
   A life buoy.

   • They threw him a lifesaver and then hauled him up onto the boat.
5. •
   Any lifesaving tool or item of supplies.

   • When I got lost in the woods, my Swiss Army knife was a lifesaver.