The antonym for thoughtful is ‘thoughtless.’
‘Thoughtful’ describes someone who is considerate and reflective, often showing care and concern for others. On the other hand, ‘thoughtless’ refers to someone who acts without consideration for the feelings or needs of others, often resulting in unkind or inconsiderate behavior. While ‘thoughtful’ embodies attentiveness and mindfulness, ‘thoughtless’ indicates a lack of awareness and sensitivity.