The Collaborative International Dictionary of English v.0.48:

Distrustful \Dis*trust"ful\, a.
   1. Not confident; diffident; wanting confidence or thrust;
      modest; as, distrustful of ourselves, of one's powers.
      [1913 Webster]

            Distrustful sense with modest caution speaks.
                                                  --Pope.
      [1913 Webster]

   2. Apt to distrust; suspicious; mistrustful. --Boyle. --
      Dis*trust"ful*ly, adv. -- Dis*trust"ful*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

distrustfulness
    n 1: the trait of not trusting others [syn: distrust,
         distrustfulness, mistrust] [ant: trust,
         trustfulness, trustingness]