cork jacket vs life preserver

cork jacket and life preserver both are nouns.

Word	Noun	Adjective	Verb	Adverb
cork jacket	Yes	No	No	No
life preserver	Yes	No	No	No

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

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

Other hypernyms of cork jacket include flotation device, preserver.

cork jacket (noun)	life preserver (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