black magic vs necromancy

black magic and necromancy both are nouns.

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

As nouns, black magic and necromancy are synonyms defined as:

black magic and necromancy: the belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world

Other synonyms of black magic include black art, sorcery.

black magic (noun)	necromancy (noun)
the belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world	conjuring up the dead, especially for prophesying
	the belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world