Definition of diabolical adjective from the Oxford Advanced American Dictionary

     

    diabolical

     adjective
    adjective
    NAmE//ˌdaɪəˈbɑlɪkl//
     
     
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  1. 1 (diabolic
    NAmE//ˌdaɪəˈbɑlɪk//
     
    )
    morally bad and evil; like a devil
  2. 2 (informal) extremely bad or annoying synonym terrible The traffic was diabolical.
diabolically
 
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NAmE//ˌdaɪəˈbɑlɪkli//
 
adverb
See the Oxford Advanced Learner's Dictionary entry: diabolical