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]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "wistful":
   ashamed, atrabiliar, atrabilious, blue, cogitative, cognitive,
   concentrating, concentrative, conceptive, conceptual,
   conceptualized, conscience-smitten, conscience-stricken,
   contemplating, contemplative, deliberating, deliberative,
   excogitating, full of remorse, funky, hankering, homesick, honing,
   ideative, introspective, languishing, longing, meditating,
   meditative, melancholic, melancholy, mental, museful, musing,
   noetic, nostalgic, pensive, pining, pondering, prehensive,
   reflecting, reflective, regretful, remorseful, repining, rueful,
   ruminant, ruminating, ruminative, self-accusing, self-condemning,
   self-convicting, self-debasing, self-flagellating,
   self-humiliating, self-punishing, self-reproaching, serious,
   shamefaced, shamefast, shameful, sober, sorry, speculative,
   thinking, thought, thoughtful, tristful, unhappy about, wishful,
   yearnful, yearning