black art vs diabolism

black art and diabolism both are nouns.

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

As nouns, diabolism is a hyponym of black art; that is, diabolism 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
diabolism: a belief in and reverence for devils (especially Satan)

Other hyponyms of black art include witchcraft, witchery, bewitchment, enchantment, demonism, Satanism, obiism.

black art (noun)	diabolism (noun)
the belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world	a belief in and reverence for devils (especially Satan)