life belt vs flotation device

life belt and flotation device both are nouns.

Word	Noun	Adjective	Verb	Adverb
life belt	Yes	No	No	No
flotation device	Yes	No	No	No

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

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

Other hypernyms of life belt include life preserver, preserver.

life belt (noun)	flotation device (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