untouchable vs unassailable

untouchable is a noun but unassailable is not a noun.

Word	Noun	Adjective	Verb	Adverb
untouchable	Yes	Yes	No	No
unassailable	No	Yes	No	No

As adjectives, untouchable and unassailable are synonyms defined as:

untouchable (noun)	unassailable (noun)
belongs to lowest social and ritual class in India

untouchable (adjective)	unassailable (adjective)
forbidden to the touch	without flaws or loopholes
impossible to assail	impossible to assail
beyond the reach of criticism or attack or impeachment	immune to attack; incapable of being tampered with
not capable of being obtained
(especially used in traditional Hindu belief of the lowest caste or castes) defiling