witchery vs necromancy

witchery and necromancy both are nouns.

Word	Noun	Adjective	Verb	Adverb
witchery	Yes	No	No	No
necromancy	Yes	No	No	No

As nouns, necromancy is a hypernym of witchery; that is, necromancy is a word with a broader meaning than witchery:

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

Other hypernyms of witchery include black art, black magic, sorcery.

witchery (noun)	necromancy (noun)
the art of sorcery	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