life belt vs life preserver

life belt and life preserver both are nouns.

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

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

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

Other hypernyms of life belt include flotation device, preserver.

life belt (noun)	life preserver (noun)
a life preserver in the form of a ring of buoyant material	rescue equipment consisting of a buoyant belt or jacket to keep a person from drowning
belt attaching you to some object as a restraint in order to prevent you from getting hurt