WordNet sense 1 (a prejudice (especially in Polynesia and other South Pacific islands) that prohibits the use or mention of something because of its sacred nature):

taboo

WordNet sense 2 (concerned with religion or religious purposes):

sacred

WordNet sense 3 (excluded from use or mention):

forbidden, out, verboten, prohibited, proscribed

WordNet sense 4 (not permitted):

impermissible