witches' brew vs smorgasbord

witches' brew and smorgasbord both are nouns.

Word	Noun	Adjective	Verb	Adverb
witches' brew	Yes	No	No	No
smorgasbord	Yes	No	No	No

As nouns, smorgasbord is a hypernym of witches' brew; that is, smorgasbord is a word with a broader meaning than witches' brew:

Other hypernyms of witches' brew include assortment, miscellanea, miscellany, mixed bag, mixture, motley, potpourri, salmagundi, variety.

witches' brew (noun)	smorgasbord (noun)
a fearsome mixture	an assortment of foods starting with herring or smoked eel or salmon etc with bread and butter; then cheeses and eggs and pickled vegetables and aspics; finally hot foods; served as a buffet meal
	a collection containing a variety of sorts of things