Taboo. Celtic society, and therefore mythology, abounds in prohibitions, taboos, or bonds that, when placed on a person or persons, compel them to obey instructions. From the sagas, as well as the Celtic law systems, the taboos come down primarily as a modus operandi put at the disposal of the druids to ensure their authority and the efficacy of their edicts. In Ireland they had two particular powers: the geis and the glam dicin. The geis tended to be more complex. It was primarily a prohibition imposed on a particular person and, since it influenced the whole fate of that person, it could not be cast or imposed lightly. Anyone transgressing a geis was exposed to the rejection of his society and placed outside the social order. Transgression, in addition to bringing shame and outlawry, usually meant a painful death. The power of the geis was above human and divine jurisdiction and brushed aside all previous rulings, establishing a new order through the wishes of the person controlling it.
The glam dicin was a satirical incantation directed against a particular person and having the strength of obligation-in other words it is a curse that can be pronounced for such valid reasons as an infringement of divine or human laws, treason, breaking a contract, or murder. In Welsh myth, the same taboos (ysgymunbeth) exist. Several characters have "a destiny laid upon them," such as LIeu LIaw Gyffes, who has a series of taboos placed on him by his mother, Aranrhod, and Culhwch, whose step-mother places a taboo on him that causes his famous quest for Olwen. Even until recent times the Celts were keenly observant of taboos. None has been more interesting than their perception of the stars and planets. The power of the word was always uppermost in Celtic perception, and Dr. Tomas De Bhaldraithe, compiler of the modern Irish Dictionary, has argued that the names given to planets were forbidden druidic words so that the ordinary people could only refer to them by euphemisms. In Irish, for example, gealach (brighrness) is the popularly used word for the moon. Other words exist as well. Old Irish contains Isca (aesca), and this word still survives in the Manx form as eayst but nowhere else. Another Irish word for moon was re, and this, too, survives in Manx used as a combined word with that for light, shollys, in the word rehollys (moonlight). And yet another Irish word for moon, luan, is now used as An Luan as the name of the moon-day, or Monday. This word is thought to derive from the native Irish word for "radiance" rather than being a loan-word from the Latin luna. So here are four distinct words for moon, all being euphemisms rather than a proper name.
We can turn to Manx for a practical example of taboo names with this regard. In the nineteenth century, when Manx fishermen set foot on shipboard they were under a taboo (a superstition imposed by folklore) not to use the word eayst for moon until they returned to land. Until then they would refer to the moon as ben-reine ny hoie (queen of the night). Likewise, the sun was only referred to as gloyr na laa (glory of the day) and not as grian. In Old and Middle Irish we find several words for the sun also: as well as the modern word grian, we have lo-chrann (head of the day), still in use in Scottish Gaelic. The same word in modern Irish becomes the word for bright, brilliance, gleaming, guiding light, and leader. We also have re-an-la (light of the day), which is also used as ree yn Id. It is interesting to note that while the ancient Celts (who were renowned for their ability in astronomy) must have had their own native names for the planets and stars, it is the Arabic, Greek, and Latin names that have been adopted into their languages. This supports the argument that there was initially a druidic proscription that continued into the period of early Christianity. Therefore, the native names by which the planets were known, the names of the stars that played so central a part in people's lives, continued as a taboo on the population. Therefore, when scribes began to write in Irish and Welsh, they eagerly accepted the foreign loan-words as euphemisms for their own proscribed names, and thus these names have been lost. Or have they?
Only in Manx Gaelic do we have the survival of the native names of two planets. In Manx, which developed away from Old Irish from the fifth and sixth centuries but did not emerge as its own developed written language until the seventeenth century, words for Mercury and Venus occur. There are two names for Mercury- Yn Curain and Yn Crean. Likewise, there are two names for Venus- Yn Vadlag and Yn Vaytnag. These survivals confirm the existence of earlier native names for the planets, which have now been lost because of the proscription against their use.

Tadhg. [I] Son of Cian of Munster. Cormac Mac Art promised to reward Tadhg's alliance against Ulster with any land that he could circumnavigate in his chariot after the battle. Cormac knew that Tadhg wanted Temuir (Tara) and the High Kingship itself, so he bribed Tadhg's charioteer to make a circumnavigation in the shape of an "L," which excluded Temuir. The story of "The Adventures ofTadhg, son of Cian, son of Ailill Olum" is thought to date back to the third century A.D., and in this voyage tale the goddess Cliodhna appears to him.  There is a second Tadhg who appears, the son of Nuada. He was a druid and father of Murna of the White Neck, mother of Fionn Mac Cumhail. He opposed the marriage of his daughter to Cumal and persuaded Conn, the High King, to send warriors after them when they eloped. Cumal was killed, but not before Murna became pregnant with Fionn.

Tailltinn, Batlle of. [I] A great battle between the De Danaan and the Milesians in which three kings and three queens of the De Danaan were slain.

Tailtu. [I] Daughter of the Firbolg king of the Great Plain, she became foster mother to Lugh Lamhfada and gave her name to Tailltinn (Anglicised as Teltown). She cleared the forest of Breg and died as a result of her labours. Lugh decreed a feast in her honour, which became known as Lughnasadh (August 1). At the feast, official games that correspond to the Olympics of ancient Greece were held. The last games were held on August 1, 1169, under the jurisdiction of the last High King, Ruraidh O Conchobhar.

Tain. [I] A cattle raid. There are several of these tales in Irish mythology , but the two most famous ones are the Tain Bo Cuailgne and the Tain Bo Fraoch. The Tain Bo Cuailgne is the most famous epic in Irish mythology, comparable to the Iliad. The basic texts are found in Leabhar na h-Uidhre (eleventh century Book of the Dun Cow) and Leabhar Laighnech (twelfth century Book of Leinster). Both versions are incomplete and additions are found in the Yellow Book of Lecan. The saga popularly describes the campaign by Medb of Connacht to capture the famous Brown Bill of Cuailgne in Ulster. The Ulster warriors are prevented from defending themselves against her army by a strange debiliry placed on them by Macha, goddess of war. Only Cuchulainn is able to carry on a defence until the Ulster warriors recover. It is the longest, most elaborate and powerful of all the Irish myths, and is the central theme of the Red Branch cycle. The Tain Bo Fraoch is the second most popular cattle raid tale. Professor C. W. von Sydow [Beowulfskalden och nordisk tradition, Arsbok, 1923] suggests that the story provided the model for the later English saga of Beowulf There are many points of similariry between the two sagas. The story concerns Fraoch, the most handsome warrior in Ireland, who sets out to woo Findbhair, daughter of Ailill and Medb.

Taliesin. [W] "Shilling Brow." A quasi-mythical figure, said to be the greatest of the bards, living during the sixth century A.D. He is claimed as the first bard to acquire the secret of prophetic poetry. He could divine the future and strike less gifted poets dumb. In the myths he is Gwion Bach reborn and his mother is the magician Ceridwen, who swallowed Gwion Bach in the form of a grain of wheat. Taliesin is rescued ftom the sea by Elffin and, at the age of thirteen, is able to dumbfound Arthur's bards. "I am old, I am new ...I have been dead, I have been alive. ..I am Taliesin." [ Chwedl Taliesin, vol. I, Williams, Cardiff, 1957.] His song is rather similar in style and import to that of the druid Amairgin.

Taliesin, Book of. [The Book of Taliesin, ed. J. G. Evans, Llanbedrog, 1910.] A collection of poetic tradition associated with Taliesin.

Tanaiste. [I] The successor to a king or professional man elected during his predecessor's lifetime.