life vest vs air jacket

life vest and air jacket both are nouns.

Word	Noun	Adjective	Verb	Adverb
life vest	Yes	No	No	No
air jacket	Yes	No	No	No

As nouns, air jacket is a hyponym of life vest; that is, air jacket is a word with a more specific, narrower meaning than life vest:

life vest: life preserver consisting of a sleeveless jacket of buoyant or inflatable design
air jacket: an inflatable life jacket

Other hyponyms of life vest include Mae West.

life vest (noun)	air jacket (noun)
life preserver consisting of a sleeveless jacket of buoyant or inflatable design	an inflatable life jacket