The Collaborative International Dictionary of English v.0.48:

Wistful \Wist"ful\, a. [For wishful; perhaps influenced by
   wistly, which is probably corrupted from OE. wisly certainly
   (from Icel. viss certain, akin to E. wit). See Wish.]
   [1913 Webster]
   1. Longing; wishful; desirous.
      [1913 Webster]

            Lifting up one of my sashes, I cast many a wistful,
            melancholy look towards the sea.      --Swift.
      [1913 Webster]

   2. Full of thought; eagerly attentive; meditative; musing;
      pensive; contemplative.
      [1913 Webster]

            That he who there at such an hour hath been,
            Will wistful linger on that hallowed spot. --Byron.
      [1913 Webster] -- Wist"ful*ly, adv. -- Wist"ful*ness,
      n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

wistful
    adj 1: showing pensive sadness; "the sensitive and wistful
           response of a poet to the gentler phases of beauty" [syn:
           pensive, wistful]