The Collaborative International Dictionary of English v.0.48:

Thoughtful \Thought"ful\, a.
   1. Full of thought; employed in meditation; contemplative;
      as, a man of thoughtful mind.
      [1913 Webster]

            War, horrid war, your thoughtful walks invades.
                                                  --Pope.
      [1913 Webster]

   2. Attentive; careful; exercising the judgment; having the
      mind directed to an object; as, thoughtful of gain;
      thoughtful in seeking truth. --Glanvill.
      [1913 Webster]

   3. Anxious; solicitous; concerned.
      [1913 Webster]

            Around her crowd distrust, and doubt, and fear,
            And thoughtful foresight, and tormenting care.
                                                  --Prior.
      [1913 Webster]

   Syn: Considerate; deliberate; contemplative; attentive;
        careful; wary; circumspect; reflective; discreet.

   Usage: Thoughtful, Considerate. He who is habitually
          thoughtful rarely neglects his duty or his true
          interest; he who is considerate pauses to reflect and
          guard himself against error. One who is not thoughtful
          by nature, if he can be made considerate, will usually
          be guarded against serious mistakes. "He who is
          thoughtful does not forget his duty; he who is
          considerate pauses, and considers properly what is his
          duty. It is a recommendation to a subordinate person
          to be thoughtful in doing what is wished of him; it is
          the recommendation of a confidential person to be
          considerate, as he has often to judge according to his
          own discretion." --Crabb.
          [1913 Webster] -- Thought"ful*ly, adv. --
          Thought"ful*ness, n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

thoughtful
    adj 1: having intellectual depth; "a deeply thoughtful essay"
    2: exhibiting or characterized by careful thought; "a thoughtful
       paper" [ant: thoughtless]
    3: acting with or showing thought and good sense; "a sensible
       young man" [syn: thoughtful, serious-minded]
    4: taking heed; giving close and thoughtful attention; "heedful
       of the warnings"; "so heedful a writer"; "heedful of what
       they were doing" [syn: heedful, attentive, thoughtful,
       paying attention] [ant: heedless, unheeding]
    5: considerate of the feelings or well-being of others

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "thoughtful":
   accommodating, accommodative, affable, agreeable, analytical,
   attentive, brainy, brooding, calculating, careful, caring,
   cautious, charitable, circumspect, civil, cogitative, cognitive,
   compassionate, complaisant, concentrating, concentrative,
   conceptive, conceptual, conceptualized, considerate, contemplating,
   contemplative, courteous, curious, decorous, deep, deferential,
   deliberating, deliberative, delicate, demure, discreet,
   discriminating, discriminative, earnest, engrossed, enlightened,
   excogitating, fair, formal, frowning, graceful, gracious, grave,
   grim, grim-faced, grim-visaged, heedful, helpful, ideative,
   indulgent, intellectual, introspective, judgmatic, judicial,
   judicious, kind, kindly, lenient, logical, long-faced, loving,
   meditating, meditative, melancholy, mental, mindful,
   mindful of others, museful, musing, noetic, obliging, pensive,
   polite, politic, pondering, prehensive, provident, prudent,
   prudential, rapt, rational, reflecting, reflective, regardful,
   respectful, ruminant, ruminating, ruminative, sedate, serious,
   sober, sober-minded, sobersided, solemn, solicitous, somber,
   speculative, staid, stone-faced, straight-faced, studious,
   sympathetic, tactful, tender, thinking, thought, tolerant,
   unsmiling, unthoughtful, urbane, wary, weighty, well-advised,
   well-judged, wistful