black magic vs witchery

black magic and witchery both are nouns.

Word	Noun	Adjective	Verb	Adverb
black magic	Yes	No	No	No
witchery	Yes	No	No	No

As nouns, witchery is a hyponym of black magic; that is, witchery is a word with a more specific, narrower meaning than black magic:

black magic: the belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world
witchery: the art of sorcery

Other hyponyms of black magic include witchcraft, bewitchment, enchantment, demonism, diabolism, Satanism, obiism.

black magic (noun)	witchery (noun)
the belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world	the art of sorcery