The antonyms for the word "un-thoughtfulness" can be many, depending on the aspect of thoughtfulness or consideration that you want to convey. Some of the opposite terms for un-thoughtfulness can include consideration, attentiveness, regard, kindness, benevolence, generosity, mindfulness, and thoughtfulness itself. A person who is not un-thoughtful is considerate of others' feelings, thinks before speaking or acting, remembers important dates or events, shows empathy and compassion, and does not push their own needs and preferences above others. Being thoughtful is an essential quality that fosters positive relationships, creates trust and respect, and promotes harmony and happiness in our personal and professional lives.