water jacket vs vessel

water jacket and vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
water jacket	Yes	No	No	No
vessel	Yes	No	No	No

As nouns, vessel is a hypernym of water jacket; that is, vessel is a word with a broader meaning than water jacket:

water jacket: a container filled with water that surrounds a machine to cool it; especially that surrounding the cylinder block of an engine
vessel: an object used as a container (especially for liquids)

water jacket (noun)	vessel (noun)
a container filled with water that surrounds a machine to cool it; especially that surrounding the cylinder block of an engine	a craft designed for water transportation
	an object used as a container (especially for liquids)
	a tube in which a body fluid circulates