1. thoughtless (vs. thoughtful), inconsiderate, unconsidered, unreflective, unthinking, unthoughtful, inconsiderate

usage: showing lack of careful thought; "the debate turned into thoughtless bickering"

2. thoughtless, uncaring, unthinking, inconsiderate (vs. considerate)

usage: without care or thought for others; "the thoughtless saying of a great princess on being informed that the people had no bread; `Let them eat cake'"

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See also: thoughtless (Dictionary)