The Collaborative International Dictionary of English v.0.48:

Untouchable \Untouchable\
   See touchable.

WordNet (r) 3.0 (2006):

untouchable
    adj 1: beyond the reach of criticism or attack or impeachment;
           "for the first time criticism was directed at a hitherto
           untouchable target"- Newsweek
    2: impossible to assail [syn: unassailable, untouchable]
    3: forbidden to the touch; "in most museums such articles are
       untouchable"
    4: ( especially used in traditional Hindu belief of the lowest
       caste or castes) defiling
    5: not capable of being obtained; "a rare work, today almost
       inaccessible"; "timber is virtually unobtainable in the
       islands"; "untouchable resources buried deep within the
       earth" [syn: inaccessible, unobtainable, unprocurable,
       untouchable]
    n 1: belongs to lowest social and ritual class in India [syn:
         untouchable, Harijan]

Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "untouchable":
   DP, Ishmael, affectless, anesthetized, antipodean, arctic,
   autistic, awesome, awful, back of beyond, banned, barred, blunt,
   castaway, catatonic, chill, chilly, cold, cold as charity,
   cold-blooded, coldhearted, contraband, cool, declasse, derelict,
   dispassionate, displaced person, divine, drugged, dull,
   emotionally dead, emotionless, evictee, exile, expatriate,
   expellee, forbade, forbid, forbidden, frigid, frosted, frosty,
   frozen, godforsaken, heartless, heavenly, holy, hyperborean, icy,
   illegal, illicit, immovable, impassible, impassive, inaccessible,
   ineffable, inenarrable, inexcitable, inexpressible, insusceptible,
   inviolable, inviolate, leper, nonemotional, nonpermissible,
   not permitted, numinous, objective, obtuse, off limits,
   out of bounds, out of reach, out of touch, out-of-the-way, outcast,
   outcast of society, outcaste, outlaw, outlawed, outsider, pariah,
   passionless, persona non grata, prohibited, religious, ruled out,
   sacred, sacrosanct, self-absorbed, social outcast, soulless,
   spiritless, spiritual, taboo, tabooed, unacceptable person,
   unaffectionate, unallowed, unapproachable, unauthorized,
   under the ban, undesirable, unemotional, unfeeling, ungetatable,
   unimpassioned, unimpressionable, unlawful, unlicensed, unloving,
   unpassionate, unpermissible, unresponding, unresponsive,
   unsanctioned, unspeakable, unsusceptible, unsympathetic,
   unutterable, venerable, verboten, vetoed