Marked by or showing lack of due thought or care; careless. (adjective)
Inconsiderate, inattentive. (adjective)
Lacking thought or consideration. (adjective)
Examples of word thoughtless
There is never a need to deny the harm that ignorance can cause, and use of the term thoughtless usually refers to some action taken without thoughtful consideration.
It's what I call thoughtless safety, and it brings you about 3 1-2 per cent, as I have already shown you.
Thoughtlessness is an attribute grounded on the facts which we call thoughtless actions; and the proposition is equivalent to this,
Thoughtlessness is an attribute, grounded on the facts which we call thoughtless actions; and the proposition is equivalent to this,
You, whom she had known from an infant, whom she had seen grow up from a period when her notice was an honour, to have you now, in thoughtless spirits, and the pride of the moment, laugh at her, humble her [...] and before others, many of whom (certainly some,) would be entirely guided by your treatment of her.