1. [n]  belongs to lowest social and ritual class in India
2. [adj]  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"
3. [adj]  defiling to the touch; especially used in traditional Hindu belief of the lowest caste or castes
4. [adj]  forbidden to the touch; "in most museums such articles are untouchable"
5. [adj]  impossible to assail
6. [adj]  beyond the reach of criticism or attack or impeachment; "for the first time criticism was directed at a hitherto untouchable target"- Newsweek

UNTOUCHABLE is a 11 letter word that starts with U.