Synonyms for Thoughtless (same or very similar meaning)
WordNet sense 1 (not exhibiting or characterized by careful thought):
unthinking, unreflective, unthoughtful
WordNet sense 2 (without proper consideration or reflection):
inconsiderate
WordNet sense 3 ((usually followed by `to') unwilling or refusing to pay heed):
indifferent
WordNet sense 4 ((usually followed by `of') without due thought or consideration):
careless, regardless
WordNet sense 5 (marked by or paying little heed or attention):
heedless, unheeding
WordNet sense 6 (without care or thought for others):
uncaring
From the ODE community, based on WordNet
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