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1. Exhibiting or characterized by careful thought
   "a thoughtful paper"
    
2. Taking heed; giving close and thoughtful attention
   - heedful, attentive, paying attention
    
3. Having intellectual depth
   "a deeply thoughtful essay"
    
4. Characterized by solemn, sincere manner
   - serious-minded
    
5. Considerate of the feelings or well-being of others

See also: attentiveness, bemused, brooding, broody, cogitative, considerate, contemplative, deliberative, excogitative, heed, lost, meditative, musing, paying attention, pensive, pondering, preoccupied, profound, reflective, regard, ruminative, serious, thoughtfulness, well thought out

Antonym: heedless, thoughtless

Encyclopedia: Thoughtful