The Collaborative International Dictionary of English v.0.48:

Confidential \Con`fi*den"tial\, a. [Cf. F. confidentiel.]
   1. Enjoying, or treated with, confidence; trusted in;
      trustworthy; as, a confidential servant or clerk.
      [1913 Webster]

   2. Communicated in confidence; secret. "Confidential
      messages." --Burke.
      [1913 Webster]

   Confidential communication (Law) See Privileged
      communication, under Privileged.

   Confidential creditors, those whose claims are of such a
      character that they are entitled to be paid before other
      creditors.

   Confidential debts, debts incurred for borrowed money, and
      regarded as having a claim to be paid before other debts.
      --McElrath.
      [1913 Webster]