a. [ Pref. ir- not + responsible: cf. F. irresponsable. ] 1. Not responsible; not liable or able to answer for consequences; innocent. [ 1913 Webster ]
2. Not to be trusted; unreliable; lacking a proper sense of responsibility. [ 1913 Webster ]
n. the habitual failure to behave in a responsible manner; irresponsibility. Syn. -- irresponsibility. [ WordNet 1.5 ]