Ocean-sweeper. [I] Aigean scuabadoir. A magical ship that knew a man's thoughts and was propelled without sails or oars wherever he willed it. Lugh Lamhfada brought it from the Otherworld. It was given as a gift to Manannan Mac Lir.

Ochain. [I] The "Moaner." Enchanted shield of Conchobhar Mac Nessa that moaned whenever its owner was in danger.

Ochall Ochne. [I] King of the sidhe of Connacht, whose swineherd was Friuch, who was in perpetual rivalry with Nar, the swineherd of Bodb Dearg of Munster.

Octriallach. [I] Son of Indech of the Fomorii, killed by Ogma at the second battle of Magh Tuireadh. He had been able to discover how Dian cecht, the De Danaan god of medicine, was able to bring back the slain De Danaan to life by the use of a magical "Spring of Health." Octriallach led the Fomorii in filling in the spring by placing great rocks over it.

Odras. [I] Daughter of Odarnatan, keeper of the hostel of Buchat Buasach. The Morrigan turned her into a pool of water.

Ogham. [I] Sometimes Ogam. The earliest form of Irish writing, frequently referred to in Irish myths and sagas. Its invention is ascribed to Ogma, god of eloquence and literature. The sagas contain many references to great libraries of bark and wands carved with the Ogham script. However, the bulk of surviving Ogham scripts, dating from the fifth and sixth centuries A.D., are recorded on stones. There are 369 such inscriptions, some found in Wales, Scotland, and Ireland, but the bulk are in Ireland, and of these the highest density is in southern Ireland, with 121 of them in Co. Kerry alone. Mairtin O Murchu [ The Irish Language, Dublin, 1985] suggests that Ogham originated in southwest Ireland. A text from the fourteen century, Book of Ballymote, is devoted to Ogham and gives an explanation of the characters. The most easterly Ogham inscription is recorded on stone at the site of Silchester. This was the tribal capital of the Celtic Atrebates (Calleva Atrebatum, according to the Romans), which, during the Roman occupation, became a walled town. After the occupation it would appear that Irish settlers, or eatly Christian missionaries, settled and put up an Ogham inscription. Then, with the invasion of the Anglo-Saxons, the Celts abandoned the town.

Ogma. [I] God of eloquence and literature. A son of the Dagda. He was skilled in dialects and poetry as well as being a warrior. He also had a role in conveying souls to the Otherwotld. He was called Ogma Grian-aineach (of the Sunny Countenance) and Ogma Cermait (of the Honeyed Mouth). He is credited with the invention of the Ogham script. He is also credited with various children, of which his daughter Etain married the god of medicine, Dian cecht. He ruled from the sldhe of Airceltrai.

Ogmia. The name found on a piece of pottery at Richborough, in England, depicting a figure with long curly hair and sun rays emanating from his head. He also holds the whip of the Sol Invictus. This is obviously the British equivalent of Ogma and Ogmios. Ogmios. The Gaulish god cognate with Ogma in Irish mythology . Lucian identified him as a Celtic Heracles. Ogmios was thought to transport the dead to the Otherworld, although Bile also had this role.

Oillipheist. [I] A fabulous beast whose passage westward caused the River Shannon to be formed.

Oilmelc. [I] The alternative name for Imbolg, meaning "sheep's milk."

Oirbsen. [I] An alternative name for Manannin Mac Lir. Loch Oirbsen was an ancient name for Loch Corrib, Co. Galway, where the ocean god is said to have met his death by drowning.

Oireachtas. [I] An assembly. An annual gathering organised by Cohradh na Gaeilge, founded in 1893, and similar to the Welsh Eisteddfod.

Oisin. [I] Ossian in Scotland and Oshin in the Isle of Man. Son of Fionn Mac Cumhail and the goddess Sadb, daughter of the Bodb Dearg. He was acknowledged as the greatest warrior in Ireland and a great warrior of the Fianna. He was found by his father, who was searching for Sadb, who had been turned into a deer. Fionn called him Oisin, or "fawn." He grew up to be one of the leading champions of the Fianna. He married a yellow-haired stranger from a sunny country named Eibhir. His most famous son was the warrior Oscar. Oisfn took part in many of the adventures of the Fianna but refused to help Fionn exact vengeance on the lovers Diarmuid and Griinne. He consorted with Niamh, a goddess from the Otherworld, and dwelt there with her for three hundred years-a period that seemed like only three weeks to him. The Fenian Cycle is often referred to as the Ossianic Cycle. The tales were made famous by the Scot James MacPherson, whose rendering of them under the general titleOssian became a European classic and started the Romantic Movement.

Ol[W] The best tracker in Britain at Arthur's fortress.

Ollamh. [I] Sometimes given as Ollave. Of the seven grades of poets, it was the highest grade. It took candidates nine to twelve years of study, for they had to memorise 250 prime storjes and 100 secondary stories to claim the title. Ollamh Fodhla was the eighteenth High King of Ireland, reigning in 714 B.C., and is traditionally recognised as founding rule by legislature and giving the country the first codified law system. He is said to have been buried at Tailltinn (Teltown, Co. Westmeath).