Worship of or devotion to the devil; belief in or practice of evil; extremely wicked behavior or attitude.
From diabolic + -ism (a suffix indicating a system of belief or practice, from Greek -ismos), following patterns like 'atheism' or 'heroism' that name ideologies or practices.
The -ism suffix is fascinating because it can mean both 'a system of belief' (like Buddhism) and 'a negative quality' (like racism or ageism)—context determines which meaning applies!
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