melting pot vs vessel

melting pot and vessel both are nouns.

Word	Noun	Adjective	Verb	Adverb
melting pot	Yes	No	No	No
vessel	Yes	No	No	No

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

melting pot: a vessel made of material that does not melt easily; used for high temperature chemical reactions
vessel: an object used as a container (especially for liquids)

melting pot (noun)	vessel (noun)
a vessel made of material that does not melt easily; used for high temperature chemical reactions	a craft designed for water transportation
an environment in which many ideas and races are socially assimilated	an object used as a container (especially for liquids)
	a tube in which a body fluid circulates