confidential

Kept, or meant to be kept, secret within a certain circle of persons; not intended to be known publicly

The newspaper claims a leaked confidential report by the government admits to problems with corrupt MPs.

[…] I have a communication of a very private—indeed, I will say, of a sacredly confidential nature, which I desire to make to you.

Inclined to share confidences; (of things) making people inclined to share confidences; involving the sharing of confidences.

Sitting in front of the fire, they became quite confidential, and began to gossip.

Long, long would it be ere Miss Crawford’s name passed his lips again, or she could hope for a renewal of such confidential intercourse as had been.

Having someone's confidence or trust; having a position requiring trust; worthy of being trusted with confidences.

a confidential agent; a confidential servant; a confidential whisper

Now, they want me to send up a confidential person with some writings.