witches' brew vs mixture

witches' brew and mixture both are nouns.

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

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

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

witches' brew (noun)	mixture (noun)
a fearsome mixture	the act of mixing together
	an event that combines things in a mixture
	any foodstuff made by combining different ingredients
	a collection containing a variety of sorts of things
	(chemistry) a substance consisting of two or more substances mixed together (not in fixed proportions and not with chemical bonding)