not paying enough attention to what you are doing, so that you make mistakes, damage things etc [≠ careful]:
It was careless of him to leave the door unlocked.
a careless mistake
He's careless with his glasses and has lost three pairs.
Careless talk can be disastrous for a business.
2 [usually before noun]
natural and not done with any deliberate effort or attention:
He ran a hand through his hair with a careless gesture.
not concerned about something
a man careless of his own safety
She gave a careless shrug.
! Do not use careless to mean that someone has no worries. Use carefree: They all felt happy and carefree.
—carelessness noun [uncountable]