fù​xīn​zhī​huàn

serious internal threat

  1. key parts
    (literary) the vital organs; metaphorically refers to central or strategic regions, specifically those most vital to security or control
  2. zhī particle
    [possessive]
    Connects a describing word or phrase to the noun it describes, similar to de but used in formal or literary writing.
  3. huàn adjectivenoun
    misfortune
    (bound form) disaster; calamity; peril; trouble