Source : Webster's Revised Unabridged Dictionary (1913)

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

   2. Communicated in confidence; secret. ``Confidential
      messages.'' --Burke.

   {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.

Source : WordNet®

confidential
     adj 1: entrusted with private information and the confidence of
            another; "a confidential secretary"
     2: (of information) given in confidence or in secret; "closet
        information"; "this arrangement must be kept
        confidential"; "their secret communications" [syn: {closet(a)},
         {secret}]
     3: denoting confidence or intimacy; "a confidential approach";
        "in confidential tone of voice"
     4: the level of official classification for documents next
        above restricted and below secret; available only to
        persons authorized to see documents so classified