noun

• (uncountable) Worship of the devil; Satanism
  "The Witchcraft Reader By Darren Oldridge In a small minority of Italian trials, one finds a mixture of charges that cannot be categorized as either sorcery or typical diabolism."
• (countable) Character, action, utterances, creative works, behavior or principles appropriate to the devil.
  ""The Fiend's Delight" By Dod Grile The atrocities constituting this "cold collation" of diabolisms are taken mainly from various Californian journals."
• (uncountable) Possession by Satan or other demonic forces.
  "And this new Donation of the ecstacies of the Saints was a noble foundation for what he was now projecting , the Farce of DIABOLISM and EXORCISMS. "Religion and Society in Latin America""
• (uncountable) The property of having attributes that are demonic or Satanic.
  "By Authors Possessed: The Demonic Novel in Russia By Adam Weiner Bely's attribution of an "Ahrimanian" spirit to Petersburg resonates on many levels of the novel, confirming not only that the core of Petersburg is diabolism, but also indicating how that diabolism relates to the novel's sense of its authorship."