1. acting without careful consideration or thought; thoughtless
2. done automatically without conscious thought

Examples

• His unthinking comment hurt her feelings deeply.
• She made an unthinking decision to quit her job without having another one lined up.
• The unthinking cruelty of children can be devastating.
• He gave an unthinking nod of agreement while reading his phone.
• Her unthinking loyalty to the company cost her better opportunities.
• The driver’s unthinking lane change caused a near accident.
• With unthinking habit, she reached for her morning coffee.