The Hebrew word ov refers to a familiar spirit — a deceased person's spirit believed to be summoned by a medium or necromancer. By extension, it also denotes the medium herself. The word appears approximately 17 times in the Old Testament, most famously in the account of the witch of Endor (1 Samuel 28).
God explicitly forbids consulting ov in the Mosaic law (Leviticus 19:31; 20:6, 27). Doing so was punishable by death because it represented a fundamental rejection of God as the only source of divine guidance. Seeking the dead defies God's sovereign authority and opens the door to demonic deception. King Saul's consultation of the medium at Endor (1 Samuel 28) stands as one of the most tragic passages in Scripture — a man who had expelled all mediums from Israel secretly turning to one in desperation, and dying the very next day. The prophet Isaiah contrasts these dark arts with seeking God directly: "When they say to you, 'Inquire of the mediums and the necromancers who chirp and mutter,' should not a people inquire of their God?" (Isaiah 8:19).