A number of scriptures refer to "familiar spirits." It was believed anciently that these particular spirits had supernatural power and could appear in human or animal form. Apparently, a familiar spirit would attend a witch, wizard, medicine man, etc., and could be called upon for service at any time by their master.
In the remote past, it was believed that these specific spirits could bring up the spirits of the dead to converse with mortals. This belief is evident in the following scripture: "And when they shall say unto you: Seek unto them that have familiar spirits, and unto wizards that peep and mutter--should not a people seek unto their God for the living to hear from the dead?" (2 Nephi 18:19; see also Isaiah 8:19) Even if familiar spirits have the power to bring up the spirits of the dead, those who truly love the Lord will seek to the Creator of Spirits to communicate with the dead rather than to a source that is forbidden by Him. Under the law of Moses, Israel was commanded not to go to "a consulter with familiar spirits" (Deuteronomy 18:11). [Vicki Alder, Mysteries in the Scriptures: Enlightenment through Ancient Beliefs, pp. 264-265]