(uncountable) Belief in, or worship of demons or devils.
1699, Anthony Ashley-Cooper, 3rd Earl of Shaftesbury, Of Virtue, and the Belief of a Deity, in An Inquiry Concerning Virtue in Two Discourses, London: A. Bell et al., p. 10,
[…] if he believes more of the prevalency of an ill designing Principle than of a good one, he is then more a Daemonist than he is a Theist, and may be called a Daemonist from the side to which the balance most inclines. ¶ All these sorts both of Daemonism, Polytheism, Atheism, and Theism, may be mixed […]
(uncountable, often figurative) The quality of being demonic.
1915, Henry James, letter to Evan Charteris dated 22 January, 1915 in Percy Lubbock (ed.), The Letters of Henry James, London: Macmillan, Volume 2, p. 453,
What a pitiful horror indeed must that Ypres desolation and desecration be—a baseness of demonism.
(countable) An act or event attributed to demons or devils; an evil act.