preserver vs life ring

preserver and life ring both are nouns.

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

As nouns, life ring is a hyponym of preserver; that is, life ring is a word with a more specific, narrower meaning than preserver:

preserver: rescue equipment consisting of a buoyant belt or jacket to keep a person from drowning
life ring: a life preserver in the form of a ring of buoyant material

Other hyponyms of preserver include life belt, life buoy, lifesaver, cork jacket, life jacket, life vest, water wings.

preserver (noun)	life ring (noun)
rescue equipment consisting of a buoyant belt or jacket to keep a person from drowning	a life preserver in the form of a ring of buoyant material
a skilled worker who is employed to restore or refinish buildings or antique furniture
someone who keeps safe from harm or danger
a cook who preserves fruits or meat