The Collaborative International Dictionary of English v.0.48:

Trustful \Trust"ful\, a.
   1. Full of trust; trusting.
      [1913 Webster]

   2. Worthy of trust; faithful; trusty; trustworthy.
      [1913 Webster] -- Trust"ful*ly,adv. -- Trust"ful*ness,
      n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

trustfully
    adv 1: with trust; in a trusting manner; "she looked at her
           father trustingly" [syn: trustfully, trustingly,
           confidingly] [ant: distrustfully, mistrustfully]
    2: in a trustful manner; "his mouth grinned trustfully"