The Collaborative International Dictionary of English v.0.48:

Ingenuousness \In*gen"u*ous*ness\, n.
   1. The state or quality of being ingenuous; openness of
      heart; frankness.
      [1913 Webster]

   2. Ingenuity. [Obs.] --Fuller.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ingenuousness
    n 1: the quality of innocent naivete [syn: artlessness,
         innocence, ingenuousness, naturalness]
    2: openly straightforward or frank [ant: disingenuousness]