このことは二人だけの秘密にしておこう。
Let's keep this a secret between the two of us.
彼女は約束どおり最後まで秘密を守った。
She kept the secret to the end, just as she had promised.
会議は秘密のうちに行われた。
The meeting was held in secret.
誰にでも人に言えない秘密の一つや二つはある。
Everyone has a secret or two they can't tell anyone.