sacrosanct

adjective2

1. •
   Sacred, very holy.
2. •
   (figurative) Beyond alteration, criticism, or interference, especially due to religious sanction; inviolable.

   • It will be noted that pre-grouping routes between London and Scotland are no longer sacrosanct—for example, Glasgow St. Enoch trains no longer run necessarily to St. Pancras. — 1960