a.
Careless, heedless, rash, thoughtless, negligent, indifferent, regardless, unconcerned, inattentive, remiss, mindness, inconsiderate, uncircumspect, headlong, indiscreet, incautious, giddy, imprudent, improvident, volatile, wild, flighty, unsteady, giddy-brained, hare-brained, foolhardy, over-venturesome.