confidential

Short definition from Wiktionary

Adjective

1. 1
   Kept, or meant to be kept, secret within a certain circle of persons; not intended to be known publicly
2. 2
   Inclined to share confidences; (of things) making people inclined to share confidences; involving the sharing of confidences.
3. 3
   Having someone's confidence or trust; having a position requiring trust; worthy of being trusted with confidences.