bathing tub vs vessel

bathing tub and vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
bathing tub	Yes	No	No	No
vessel	Yes	No	No	No

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

bathing tub: a relatively large open container that you fill with water and use to wash the body
vessel: an object used as a container (especially for liquids)

bathing tub (noun)	vessel (noun)
a relatively large open container that you fill with water and use to wash the body	a craft designed for water transportation
	an object used as a container (especially for liquids)
	a tube in which a body fluid circulates