獅し子し身しん中ちゅう

noun

treacherous insider; snake in one's bosom

A yojijukugo referring to a trusted person who betrays you from within, like a parasite inside a lion. Often used in literary or cautionary contexts.

• 彼かれはまさに獅し子し身しん中ちゅうの虫むしだった。

  He was truly a snake in our bosom.

• 組そ織しきを守まもるには、獅し子し身しん中ちゅうの者ものを見み抜ぬかねばならない。

  To protect the organization, we must identify the treacherous insiders.