ewer vs vessel

ewer and vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
ewer	Yes	No	No	No
vessel	Yes	No	No	No

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

ewer (noun)	vessel (noun)
an open vessel with a handle and a spout for pouring	a craft designed for water transportation
	an object used as a container (especially for liquids)
	a tube in which a body fluid circulates