lifesaver vs life ring

lifesaver and life ring both are nouns.

Word	Noun	Adjective	Verb	Adverb
lifesaver	Yes	No	No	No
life ring	Yes	No	No	No

As nouns, lifesaver and life ring are synonyms defined as:

lifesaver and life ring: a life preserver in the form of a ring of buoyant material

Other synonyms of lifesaver include life belt, life buoy.

lifesaver (noun)	life ring (noun)
a life preserver in the form of a ring of buoyant material	a life preserver in the form of a ring of buoyant material
an attendant employed at a beach or pool to protect swimmers from accidents