Necromancy
Seeking knowledge from the dead; in the Middle Ages the word also came to mean demonic magic in general.
Also: nekyomanteia, nigromancy, raising the dead, oracle of the dead
The Greek word nekyomanteia, divination from the dead, names a practice described in Homer's Odyssey, where Odysseus pours offerings and speaks with the dead prophet Tiresias. A sanctuary of the dead at Acheron in Greece was a known place of such consultation. The Hebrew Bible tells of the medium of Endor, whom King Saul asked to call up the prophet Samuel, and forbids consulting the dead. In medieval Latin the word was altered to nigromancy, black art, and was used for any learned magic that involved spirits, which is why many grimoires were called necromantic. Today the word is mostly used in fantasy fiction, while mediumship and ancestor rites belong to living traditions.