taboo

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A ban or an inhibition resulting from social custom or emotional aversion.
2. n. A prohibition, especially in Polynesia and other South Pacific islands, excluding something from use, approach, or mention because of its sacred and inviolable nature.
3. n. An object, a word, or an act protected by such a prohibition.
4. adj. Excluded or forbidden from use, approach, or mention: a taboo subject.
5. v. To exclude from use, approach, or mention; place under taboo.

Century Dictionary and Cyclopedia

1. Among the Polynesians and other races of the South Pacific, separated or set apart either as forbidden or as sacred; placed under ban or prohibition; consecrated either to exclusion or avoidance or to special use, regard, or service; hence, in English use, forbidden; interdicted.
2. n. Among the Polynesians and other races of the South Pacific, a system, practice, or act whereby persons, things, places, actions, or words are or may be placed under a ban, curse, or prohibition, or set apart as sacred or privileged in some specific manner, usually with very severe penalties for infraction. Taboo rests primarily upon religious sanctions, but is also a civil institution; and a taboo may be applied in various ways by a priest or a chief, or even sometimes by a private person, though with limited effect. Some taboos are permanently established, especially those affecting women; a special taboo may affect any of the relations or doings of life, or any subject animate or inanimate, either permanently or for a fixed period. As an institution, taboo has ceased or is dying out in most of the regions mentioned, through European influence; but both the principle and the practice have existed or still exist to some extent, under different names, among primitive peoples generally.
3. n. Hence A prohibitory or restraining injunction or demonstration; restraint or exclusion, as from social intercourse or from use, imposed by some controlling influence; ban; prohibition; ostracism: as, to put a person or a thing under taboo. See the verb.
4. To put under taboo; disallow, or forbid the use of; interdict approach to, or contact or intercourse with; hence, to ban, exclude, or ostracize by personal authority or social influence: as, to taboo the use of tobacco; a tabooed person or subject (one not to be mentioned or discussed).

Wiktionary

1. n. An inhibition or ban that results from social custom or emotional aversion.
2. n. Something which may not be used, approached or mentioned because it is sacred.
3. adj. Excluded or forbidden from use, approach or mention.
4. v. To mark as taboo.
5. v. To ban.
6. v. To avoid.

GNU Webster's 1913

1. n. A total prohibition of intercourse with, use of, or approach to, a given person or thing under pain of death, -- an interdict of religious origin and authority, formerly common in the islands of Polynesia; interdiction.
2. v. To put under taboo; to forbid, or to forbid the use of; to interdict approach to, or use of.
3. adj. Set apart or sacred by religious custom among certain races of Polynesia, New Zealand, etc., and forbidden to certain persons or uses; hence, prohibited under severe penalties; interdicted.

WordNet 3.0

1. v. declare as sacred and forbidden
2. adj. forbidden to profane use especially in South Pacific islands
3. n. a prejudice (especially in Polynesia and other South Pacific islands) that prohibits the use or mention of something because of its sacred nature
4. n. an inhibition or ban resulting from social custom or emotional aversion
5. adj. excluded from use or mention