The Collaborative International Dictionary of English v.0.48:

Covertness \Cov"ert*ness\ (k?v"?rt-n?s), n.
   Secrecy; privacy. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

covertness
    n 1: the state of being covert and hidden [syn: hiddenness,
         covertness]