心腹事

xīnfùshì

deeply held secret

Wiktionary

Entry Composition

1 心腹 xīnfù trusted aide; confidant
=2 事 shì
  1. matter
  2. thing
  3. item
  4. work
  5. affair

classifiers: 件, 樁, 回
=2 事 zì
  1. alternative form of 倳 (zì, “to establish”)
  2. alternative form of 剚 (zì, “to stab”)