inviolable has 9 distinct synonyms spread across 3 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is violable.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
incapable of being transgressed or dishonored
“the person of the king is inviolable”
immune to attack; incapable of being tampered with
“an impregnable fortress”
must be kept sacred
Synonyms, antonyms and the broader and narrower relations for inviolable come from Princeton University’s WordNet. Full sources and licences.