The Collaborative International Dictionary of English v.0.48:

Secretiveness \Se*cret"ive*ness\, n.
   1. The quality of being secretive; disposition or tendency to
      conceal.
      [1913 Webster]

   2. (Phren.) The faculty or propensity which impels to
      reserve, secrecy, or concealment.
      [1913 Webster]

WordNet (r) 3.0 (2006):

secretiveness
    n 1: characterized by a lack of openness (especially about one's
         actions or purposes) [syn: closeness, secretiveness]
         [ant: nakedness, openness]
    2: the trait of keeping things secret [syn: secrecy,
       secretiveness, silence]