mixture vs witch's brew

mixture and witch's brew both are nouns.

Word	Noun	Adjective	Verb	Adverb
mixture	Yes	No	No	No
witch's brew	Yes	No	No	No

As nouns, witch's brew is a hyponym of mixture; that is, witch's brew is a word with a more specific, narrower meaning than mixture:

mixture (noun)	witch's brew (noun)
the act of mixing together	a fearsome mixture
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)