tiara

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An ornamental, often jeweled, crownlike semicircle worn on the head by women on formal occasions.
2. n. The triple crown worn by the pope.

Century Dictionary and Cyclopedia

1. n. An ornament or article of dress with which the ancient Persians covered the head: a kind of turban. As different authors describe it it must have been of different forms. The kings of Persia alone had a right to wear it straight or erect; lords and priests wore it depressed, or turned down on the fore side. Xenophon says the tiara was encompassed with the diadem, at least in ceremonials.
2. n. A cylindrical diadem pointed at the top, tipped with the mound and cross of sovereignty, and surrounded with three crowns, which the Pope wears as a symbol of his threefold sovereignty. Till late in the middle ages tiara was a synonym of mitra, a bishop's miter, and at ceremonies of a purely spiritual character the Pope still wears the miter, not the tiara. Cath. Dict.
3. n. Figuratively, the papal dignity.
4. n. A coronet or frontal; an ornament for the head: used loosely for any such ornament considered unusually rich: as, a tiara of brilliants.
5. n. In heraldry, a bearing representing a tall cap-like or pointed dome surrounded by three crowns, one above the other, and having at the point an orb and cross: it is supposed to represent the crown of the Pope. It is usually all of gold, and this does not need to be expressed in the blazon. Also called Pope's crown, triple crown.
6. n. In conchology: A miter-shell.
7. n. [capitalized] A genus of miter-shells.

Wiktionary

1. n. The papal crown.
2. n. An ornamental coronet.

GNU Webster's 1913

1. n. A form of headdress worn by the ancient Persians. According to Xenophon, the royal tiara was encircled with a diadem, and was high and erect, while those of the people were flexible, or had rims turned over.
2. n. The pope's triple crown. It was at first a round, high cap, but was afterward encompassed with a crown, subsequently with a second, and finally with a third. Fig.: The papal dignity.

WordNet 3.0

1. n. a jeweled headdress worn by women on formal occasions