black art vs witchery

black art and witchery both are nouns.

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

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

black art: 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 art include witchcraft, bewitchment, enchantment, demonism, diabolism, Satanism, obiism.

black art (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