witch doctor vs necromancer

witch doctor and necromancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
witch doctor	Yes	No	No	No
necromancer	Yes	No	No	No

As nouns, necromancer is a hypernym of witch doctor; that is, necromancer is a word with a broader meaning than witch doctor:

Other hypernyms of witch doctor include magician, sorcerer, thaumaturge, thaumaturgist, wizard.

witch doctor (noun)	necromancer (noun)
someone who is believed to heal through magical powers	one who practices magic or sorcery
	one who practices divination by conjuring up the dead