Demonomancy is the art of divination by summoning Demons.
From Greek daimon, divine power
The divination occurs through the oracles made by the Demons, or the answers they give to the inquirers. However, this form of divination is thought to be not very reliable because Demons are reputedly vain and unreliable. A.G.H. Each Demon is supposed to obey only if the seer uses the proper ritual.