Definition of diabolical adjective from the Oxford Advanced Learner's Dictionary

     

    diabolical

     adjective
    adjective
    BrE BrE//ˌdaɪəˈbɒlɪkl//
     
    ; NAmE NAmE//ˌdaɪəˈbɑːlɪkl//
     
    Describing annoying traits, Immoral
     
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  1. 1(informal, especially British English) extremely bad or annoying synonym terrible The traffic was diabolical. It was a diabolical performance and we felt something had to be done before the next match. See related entries: Describing annoying traits
  2. 2(less frequent diabolic
    BrE BrE//ˌdaɪəˈbɒlɪk//
     
    ; NAmE NAmE//ˌdaɪəˈbɑːlɪk//
     
    )
    morally bad and evil; like a devil See related entries: Immoral
See the Oxford Advanced American Dictionary entry: diabolical