perfidy

/ˈpɜrfɪdi/
noun
  1. The act of betraying someone's trust; deliberate dishonesty or treachery.
    • The treaty was broken by an act of perfidy that led to war.
    • He could not believe the perfidy of his best friend, who had lied to him for years.
    • In the novel, the villain's perfidy is revealed in the final chapter.
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