To make diabolic, wicked, or devilish; to represent or portray as devilish.
From diabolic + -ize (from Greek -izein, meaning 'to make'), following patterns like 'sanitize' and 'jeopardize,' where -ize transforms adjectives into action verbs.
The -ize suffix is so powerful in English that you can theoretically add it to almost any adjective—this is why 'diabolize' feels natural even if it's rarely used!
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