lacking in consideration for others; inconsiderate; tactless

a thoughtless remark.

characterized by or showing lack of thought

a shallow, thoughtless book.

not thinking enough; careless or heedless

thoughtless of his health.

devoid of or lacking capacity for thought.

adjective

considerate , kind , thinking , thoughtful , unselfish , attentive , heeding , mindful , observant

adjective

antisocial , apathetic , asocial , blind , boorish , brash , deaf , discourteous , egocentric , hasty , heedless , hot-headed , impolite , inattentive , incautious , indelicate , indifferent , indiscreet , insensitive , listless , madcap , neglectful , negligent , primitive , rash , reckless , rude , self-centered , selfish , sharp , short , tactless , uncaring , unceremonious , unconcerned , undiplomatic , ungracious , unheeding , unkind , unmindful , unrefined , bovine , careless , confused , doltish , dull , empty-headed , flighty , foolish , ill-advised , ill-considered , imprudent , inadvertent , inane , incomprehensible , inept , injudicious , irrational , irreflective , lamebrained , loony * , mindless , obtuse , puerile , regardless , remiss , senseless , silly , stupid , undiscerning , unreasonable , unreasoning , unreflective , unthinking , vacuous , witless , feckless , irresponsible , disregardful , inconsiderate , unthoughtful , incogitant