The Collaborative International Dictionary of English v.0.48:

Incorrigible \In*cor"ri*gi*ble\, a. [L. incorrigibilis: cf. F.
   incorrigible. See In- not, and Corrigible.]
   Not corrigible; incapable of being corrected or amended; bad
   beyond correction; irreclaimable; as, incorrigible error.
   "Incorrigible fools." --Dryden.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Incorrigible \In*cor"ri*gi*ble\, n.
   One who is incorrigible; a person whose persistent bad
   behavior cannot be changed; especially, a hardened criminal;
   as, the perpetual imprisonment of incorrigibles; incorrigible
   and disruptive children need to be placed in a separate
   classroom.
   [1913 Webster]

WordNet (r) 3.0 (2006):

incorrigible
    adj 1: impervious to correction by punishment [ant:
           corrigible]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "incorrigible":
   bad, beyond control, beyond recall, beyond remedy, breachy,
   chronic, confirmed, contumacious, cureless, deep-dyed, deep-fixed,
   deep-rooted, deep-seated, deep-set, deep-settled, defiant,
   dyed-in-the-wool, established, fast, fixed, fractious, gone,
   graceless, habitual, hardened, hopeless, immedicable, implanted,
   inculcated, incurable, indocile, indomitable, infixed, inflexible,
   ingrained, inoperable, instilled, insuppressible, intractable,
   inveterate, irreclaimable, irrecoverable, irredeemable,
   irreformable, irremediable, irreparable, irrepressible,
   irretrievable, irreversible, irrevocable, long-established, lost,
   naughty, obdurate, obstreperous, out of hand, past hope,
   past praying for, recalcitrant, refractory, remediless, resistant,
   resisting, restive, rooted, ruined, set, settled, settled in habit,
   shrewish, shriftless, sinful, stubborn, terminal, thorough,
   unalterable, unbiddable, unchangeable, uncontrollable, undone,
   ungovernable, unmalleable, unmanageable, unmitigable, unmoldable,
   unredeemable, unregenerate, unrelievable, unruly, unsalvable,
   unsalvageable, unsubmissive, villainous, wicked, wild