adj. 1. Marked by or showing lack of due forethought or care; careless: a thoughtless mistake; a thoughtless bumbler. See Synonyms at careless. 2. Inconsiderate of the feelings of others: a thoughtless remark. 3. Lacking thought: staring blankly in a thoughtless daze. thoughtless·ly adv. thoughtless·ness n. |
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.