The Collaborative International Dictionary of English v.0.48:

Privileged \Priv"i*leged\, a.
   Invested with a privilege; enjoying a peculiar right,
   advantage, or immunity.
   [1913 Webster]

   Privileged communication. (Law)
   (a) A communication which can not be disclosed without the
       consent of the party making it, -- such as those made by
       a client to his legal adviser, or by persons to their
       religious or medical advisers.
   (b) A communication which does not expose the party making it
       to indictment for libel, -- such as those made by persons
       communicating confidentially with a government, persons
       consulted confidentially as to the character of servants,
       etc.

   Privileged debts (Law), those to which a preference in
      payment is given out of the estate of a deceased person,
      or out of the estate of an insolvent. --Wharton.
      --Burrill.

   Privileged witnesses (Law) witnesses who are not obliged to
      testify as to certain things, as lawyers in relation to
      their dealings with their clients, and officers of state
      as to state secrets; also, by statute, clergymen and
      physicans are placed in the same category, so far as
      concerns information received by them professionally.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRIVILEGED COMMUNICATIONS. Those statements made by a client to his counsel
or attorney, or solicitor, in confidence, relating to some cause Or action
then pending or in contemplation.
     2. Such communications cannot be disclosed without the consent of the
client. 6 M. & W. 587; 8 Dow]. 774; 2 Yo. & C. 82; 1 Dowl. N. S. 651; 9
Mees. & W. 508. See Confidential communication.