Definition of arch-fiend in English:

arch-fiend

noun

literary
  • The Devil.

    • ‘This "argument" is a device of the sleepless Archfiend, the Adversary!’
    • ‘Mather was a devoted Anglican minister who completely believed in the existence of witches and demons and warned of the dangers posed to New England's "New Jerusalem" by the Archfiend, Satan himself.’
    • ‘Amelia Wilson's illustrated history of the Devil is a wonderful introduction to the myth of the Archfiend as he appears throughout history and across religions and cultures.’