WordNet sense 1 (able to withstand attack):

impregnable, secure, strong, unattackable

WordNet sense 2 (immune to attack; impregnable):

invulnerable

WordNet sense 3 (impossible to assail):

unassailable, untouchable

WordNet sense 4 (must be kept sacred):

inviolate, sacrosanct

WordNet sense 5 (concerned with religion or religious purposes):

sacred

WordNet sense 6 (not capable of being violated or infringed):

absolute, infrangible

WordNet sense 7 (incapable of being repudiated or transferred to another):

inalienable, unalienable