preserver vs lifesaver

preserver and lifesaver both are nouns.

Word	Noun	Adjective	Verb	Adverb
preserver	Yes	No	No	No
lifesaver	Yes	No	No	No

As nouns, lifesaver is a hyponym of preserver; that is, lifesaver 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
lifesaver: a life preserver in the form of a ring of buoyant material

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

preserver (noun)	lifesaver (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	an attendant employed at a beach or pool to protect swimmers from accidents
someone who keeps safe from harm or danger
a cook who preserves fruits or meat