1.showing lack of careful thought;
the debate turned into thoughtless bickering
2.marked by or paying little heed or attention;
We have always known that heedless self-interest was bad morals; we know now that it is bad economics--Franklin D. Roosevelt
3.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'
4.(usually followed by `of') without due thought or consideration;
careless of the consequences