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):

distrustful
    adj 1: having or showing distrust; "a man of distrustful
           nature"; "my experience...in other fields of law has made
           me distrustful of rules of thumb generally"- B.N.Cardozo;
           "vigilant and distrustful superintendence"- Thomas
           Jefferson [ant: trustful, trusting]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "distrustful":
   Pyrrhonic, agnostic, cagey, cautious, chary, cynical, disbelieving,
   doubtful, doubting, dubious, envious, from Missouri, green,
   green with jealousy, green-eyed, hesitant, hesitating, horn-mad,
   in doubt, invidious, jaundice-eyed, jaundiced, jealous, leery,
   mistrustful, mistrusting, nervous, questioning, sceptical,
   scrupulous, shy, skeptical, suspecting, suspicious, unbelieving,
   uncertain, uneasy, unsure, untrusting, wary, yellow, yellow-eyed