秘ひ中ちゅう

noun

in secret; secretly; confidentially

Used to indicate that something is done or kept hidden from others. Often appears in formal or written contexts.

• その計けい画かくは秘ひ中ちゅうに進すすめられた。

  The plan was carried out in secret.

• 彼かれは秘ひ中ちゅうに情じょう報ほうを集あつめていた。

  He was gathering information secretly.