cork jacket vs flotation device

cork jacket and flotation device both are nouns.

Word	Noun	Adjective	Verb	Adverb
cork jacket	Yes	No	No	No
flotation device	Yes	No	No	No

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

cork jacket: life preserver consisting of a sleeveless jacket of buoyant or inflatable design
flotation device: rescue equipment consisting of a buoyant belt or jacket to keep a person from drowning

Other hypernyms of cork jacket include life preserver, preserver.

cork jacket (noun)	flotation device (noun)
life preserver consisting of a sleeveless jacket of buoyant or inflatable design	rescue equipment consisting of a buoyant belt or jacket to keep a person from drowning