magus vs necromancer

magus and necromancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
magus	Yes	No	No	No
necromancer	Yes	No	No	No

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

Other hypernyms of magus include magician, sorcerer, thaumaturge, thaumaturgist, wizard.

magus (noun)	necromancer (noun)
a magician or sorcerer of ancient times	one who practices magic or sorcery
a member of the Zoroastrian priesthood of the ancient Persians	one who practices divination by conjuring up the dead