The Collaborative International Dictionary of English v.0.48:

Privy \Priv"y\, n.; pl. Privies.
   1. (Law) A partaker; a person having an interest in any
      action or thing; one who has an interest in an estate
      created by another; a person having an interest derived
      from a contract or conveyance to which he is not himself a
      party. The term, in its proper sense, is distinguished
      from party. --Burrill. --Wharton.
      [1913 Webster]

   2. A necessary house or place for performing excretory
      functions in private; an outhouse; a backhouse.
      [1913 Webster +PJC]