– very casual attitude
– worry-free or carefree attitude
– relaxed and not worried about the results of your actions
1. The opening batsman’s devil-may-care approach may ruin his chances of securing a permanent in the team.
2. She had a rather devil-may-care attitude towards money which impressed me at the time.
3. You must get rid of your devil-may-care attitude if you want to succeed.
4. Jane acts so uncaring with her devil-may-care manner.
5. He has a rather devil-may-care attitude to his studies.
First uses of this idioms was found in about 1765-95. But we do not have correct original details of this idiom, if you do, please post in comment below.
careless, reckless, cavalier, unconcerned, free and easy, inattentive, rash, happy-to-go, heedless, foolhardy, easygoing, nonchalant.