life ring vs life buoy

life ring and life buoy both are nouns.

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

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

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

Other synonyms of life ring include life belt, lifesaver.

life ring (noun)	life buoy (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