The word "thoughtless" is an adjective meaning lacking consideration for others' feelings or needs, or the consequences of one's actions. It can also be used adverbially as "thoughtlessly" or as a noun "thoughtlessness" to describe the state of being thoughtless.
thoughtless: adj. the quality of not thinking about other people's feelings or needs, or not considering the possible results of one's actions. It can be described as careless, inconsiderate, or thoughtless. thoughtlessly: adv. in a way that shows a lack of thought or consideration for others. thoughtlessness: n. the state or quality of being thoughtless.
[ADJ-GRADED 能被表示程度的副词或介词词组修饰的形容词]不顾及他人的；欠考虑的 If you describe someone as thoughtless, you are critical of them because they forget or ignore other people's wants, needs, or feelings.
[disapproval]
...a small minority of thoughtless and inconsiderate people...
一小群只顾自己、不顾别人的人
It was thoughtless of her to mention it...
她提起这事有些欠考虑。
It was just a thoughtless remark.
那不过是一句欠考虑的话。
thoughtlessly
They thoughtlessly planned a picnic without him...
他们太粗心，安排野餐竟然没有带上他。
Nobody is perfect, and everyone acts thoughtlessly on occasion.
人无完人，谁都难保不偶尔疏忽一次。
thoughtlessness
What women mistake as thoughtlessness is often just diffidence.
女性误以为是考虑不周的事情往往只是缺乏自信。
Oxford
thought·less/ˈθɔːtləs; NAmEˈθɔːtləs/adjective( disapproving) not caring about the possible effects of your words or actions on other people 粗心大意的；欠考虑的；轻率的SYN
not thinking about the needs and feelings of other people, especially because you are thinking about what you wantOPP thoughtful: a selfish and thoughtless manit is thoughtless of somebody to do something It was thoughtless of her not to tell you where she was going.► see thesaurus at