life buoy vs life ring

life buoy and life ring both are nouns.

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

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

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

Other synonyms of life buoy include life belt, lifesaver.

life buoy (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