guardian vs preserver

guardian and preserver both are nouns.

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

As nouns, preserver is a hypernym of guardian; that is, preserver is a word with a broader meaning than guardian:

guardian (noun)	preserver (noun)
a person who cares for persons or property	rescue equipment consisting of a buoyant belt or jacket to keep a person from drowning
	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