irresponsible

irresponsible
    adj 1: showing lack of care for consequences; "behaved like an
           irresponsible idiot"; "hasty and irresponsible action"
           [ant: {responsible}]
    

Irresponsible \Ir`re*spon"si*ble\, 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]
    

121 Moby Thesaurus words for "irresponsible":
      adrift, afloat, alternating, amorphous, capricious, carefree,
      careless, changeable, changeful, chartered, desultory, deviable,
      devil-may-care, disobedient, dizzy, eccentric, erratic, excepted,
      excused, exempt, exempted, fast and loose, favored, feckless,
      fickle, fitful, flickering, flighty, flitting, fluctuating,
      fly-by-night, freakish, giddy, headstrong, heady, immune,
      impetuous, impulsive, incautious, inconsistent, inconstant,
      indecisive, ineffectual, infirm, insubordinate, irregular,
      irresolute, lawless, let off, licensed, licentious, mazy,
      mercurial, moody, mutinous, permitted, privileged, rambling,
      rampant, rash, reckless, reinless, released, restless, roving,
      scatterbrained, self-willed, shapeless, shifting, shifty,
      shuffling, spared, spasmodic, spineless, trustless, unaccountable,
      unanswerable, unbridled, uncertain, unchecked, uncontrolled,
      uncurbed, undependable, undisciplined, unfaithworthy, unfixed,
      ungoverned, unliable, unpredictable, unreined, unreliable,
      unrestrained, unruly, unsettled, unstable, unstable as water,
      unstaid, unsteadfast, unsteady, unsubject, unsure, untrustworthy,
      untrusty, vacillating, vagrant, variable, vicissitudinary,
      vicissitudinous, volatile, wandering, wanton, wavering, wavery,
      wavy, wayward, weak, whimsical, wild, wildcat, willful,
      wishy-washy