Synonyms for Taboo (same or very similar meaning)
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):
tabu
WordNet sense 2 (concerned with religion or religious purposes):
sacred
WordNet sense 3 (excluded from use or mention):
forbidden, out, verboten, prohibited, proscribed
From the ODE community, based on WordNet
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