confidante
    n 1: a female confidant

Confidant \Con`fi*dant"\; 277), n. masc., Confidante
\Con`fi*dante"\ (?; 277), n. fem.[F. confident, confidente,
   formerly also spelt confidant, confidante. See Confide, and
   cf. Confident.]
   One to whom secrets, especially those relating to affairs of
   love, are confided or intrusted; a confidential or bosom
   friend.
   [1913 Webster]

         You love me for no other end
         Than to become my confidant and friend;
         As such I keep no secret from your sight. --Dryden.
   [1913 Webster]

CONFIDANT, CONFIDANTE, n.  One entrusted by A with the secrets of B,
confided by _him_ to C.