57 synonyms for irresponsible such as careless of one's duty, blasé, and carefree. Irresponsible is an adjective, and its antonyms are responsible, sensible, and serious.
Blasé, carefree, careless, careless of one's duty, casual, daredevil, delinquent, derelict, devil-may-care, disregardful, erratic, feather-brained, flighty, foolhardy, foolish, giddy, hare-brained, harum-scarum, hasty, heedless, hot-headed, ill-advised, ill-considered, immature, impetuous, imprudent, impulsive, inadvertent, inattentive, incautious, injudicious, insouciant, lax, misguided, naive, neglectful, negligent, oscitant, overhasty, precipitate, precipitous, rash, reckless, remiss, scatterbrained, slack, slap-happy, tearaway, thoughtless, uncaring, undependable, unheeding, unreliable, untrustworthy, unwise, and wild.