1) Belief in demons 1) Demon 2) Demonism 3) Deviltry 4) Diablerie 5) Sorcery 
Demonology is the systematic study of demons or beliefs about demons. It is the branch of theology relating to supernatural beings who are not gods. It deals both with benevolent beings that have no circle of worshippers or so limited a circle as to be below the rank of gods, and with malevolent beings of all kinds. The original sense of `demon`.....
study of demons
• (n.) A treatise on demons; a supposititious science which treats of demons and their manifestations.
(from the article `Judaism`) ...reactions against them. The speculative taste of Jewish thinkers between the 2nd century and the 1st century took them in many different ...
De`mon·ol'o·gy noun [ Demon + -logy : confer French démonologie .] A treatise on demons; a supposititious science which treats of demons and their manifestations. Sir W. Scott. 
Referring to a study of the widespread religious ideas of hostile superhuman beings called demons. These creatures were generally thought of as inhabiting a super- or under-world and playing havoc with the fortunes of man by bringing about diseases, mental twists and calamities in general. Ridding an individual supposedly held in possession by suc....
the study of demons or of beliefs about demons. · belief in demons. · a group of persons or things regarded as evil or pernicious.