taboo -
a prejudice (especially in Polynesia and other South Pacific islands) that prohibits the use or mention of something because of its sacred nature
A taboo is a strong social prohibition relating to any area of human activity or social custom that is sacred and forbidden based on moral judgment and sometimes even religious beliefs. Breaking the taboo is usually considered objectionable or abhorrent by society. The term comes from the Tongan word tabu, meaning set apart or forbidden, and appears in many Polynesian cultures.
OmegaWiki Dictionary
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taboo An inhibition or ban that results from social custom or emotional aversion.