tank vs vessel

tank and vessel both are nouns.

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

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

tank (noun)	vessel (noun)
a large (usually metallic) vessel for holding gases or liquids	a craft designed for water transportation
an enclosed armored military vehicle; has a cannon and moves on caterpillar treads	an object used as a container (especially for liquids)
a freight car that transports liquids or gases in bulk	a tube in which a body fluid circulates
a cell for violent prisoners
as much as a tank will hold

tank (verb)	vessel (verb)
treat in a tank
consume excessive amounts of alcohol
store in a tank by causing (something) to flow into it