Definition of fiendish in English:

fiendish

adjective

  • 1Extremely cruel or unpleasant.

    ‘fiendish methods of torture’
    • ‘Human beings over the ages have delighted in the most horrific and fiendish methods of inflicting extreme suffering, pain and mutilation.’
    • ‘I seem to be stuck halfway between fiendish laughter and pathetic sobbing.’
    wicked, cruel, vicious, evil, nefarious, unspeakable
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    1. 1.1informal Extremely awkward or complex.
      ‘a fiendish problem’
      • ‘She triumphed over a field of men and women of all ages with a winning time of 13 minutes 48 seconds for a super fiendish puzzle.’
      • ‘The superlatively analytical Inspector Hemingway reveals his unnerving talent for solving a fiendish problem.’
      difficult, complex, complicated, intricate, involved, knotty, thorny, ticklish, abstruse, impenetrable, unfathomable
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Pronunciation

fiendish

/ˈfiːndɪʃ/