무심해요 · 무심했어요 · 무심한 (+noun)
indifferent, uncaring, thoughtless
Example
바쁘다고 부모님께 너무 무심했던 것 같아요.
I think I've been too neglectful of my parents because I was busy.
Word parts
무 without+심 heart
Literally 'without heart' — not paying attention to others' feelings.