Irish Mythology Names

These names occur in the mythologies and legends of Ireland.
gender
usage
Áed m Old Irish, Irish Mythology
Old Irish form of Aodh.
Aífe f Irish Mythology, Old Irish
Old Irish form of Aoife.
Ailbe m & f Old Irish, Irish Mythology
Old Irish form of Ailbhe.
Ailbhe f & m Irish, Irish Mythology
From Old Irish Ailbe, possibly derived from the Celtic root *albiyo- "world, light, white" or Old Irish ail "rock". In Irish legend this was the name of a female warrior of the Fianna. It was also the name of a 6th-century male saint, the founder of a monastery at Emly.
Ailill m Old Irish, Irish Mythology
Means "elf" in Irish. This name was borne by several early Irish kings. It also occurs frequently in Irish legend, borne for example by the husband of Queen Medb. It was also the name of two saints, both bishops of Armagh in the 6th century.
Áine f Irish, Irish Mythology, Old Irish
Means "radiance, brilliance" in Irish. This was the name of a goddess of love and fertility in Irish legend, thought to dwell at the hill of Cnoc Áine in Limerick. It has sometimes been Anglicized as Anne.
Aodh m Irish, Scottish Gaelic, Irish Mythology
From Old Irish Áed, which meant "fire". This was a very popular name in early Ireland, being borne by numerous figures in Irish mythology and several high kings. It has been traditionally Anglicized as Hugh.
Aoife f Irish, Irish Mythology
From Old Irish Aífe, derived from oíph meaning "beauty" (modern Irish aoibh). This was the name of several characters in Irish legend, including a woman at war with Scáthach (her sister in some versions). She was defeated in single combat by the hero Cúchulainn, who spared her life on the condition that she bear him a child (Connla). Another legendary figure by this name appears in the Children of Lir as the jealous third wife of Lir.... [more]
Aonghus m Irish, Scottish Gaelic, Irish Mythology
From Old Irish Óengus, possibly meaning "one strength" from óen "one" and guss "force, strength". Aonghus (sometimes surnamed Mac Og meaning "young son") was an Irish god of love and youth, one of the Tuatha Dé Danann. He was the son of Dagda and Boann. The name was also borne by an 8th-century Pictish king, several Irish kings, and a few saints, including a 9th-century bishop of Tallaght.
Balor m Irish Mythology
Meaning uncertain. In Irish mythology Balor was a giant king of the Fomorians. He had an evil eye that could destroy opposing armies, though it took four men to pull open the eyelid. In battle with the Tuatha Dé Danann he slew their king Nuada, but was himself killed when the hero Lugh shot a stone into his eye.
Bébinn f Old Irish, Irish Mythology
Means "white woman", from Old Irish "woman" and finn "white, blessed". This name was borne by several characters in Irish mythology, including the mother of the hero Fráech.
Bile m Irish Mythology
Possibly an Irish form of Belenus, though it may derive from an Irish word meaning "sacred tree, scion, hero". In Irish mythology this was the name of one of the Milesians who was drowned while invading Ireland.
Bláithín f Irish, Irish Mythology
Modern Irish form of Bláthíne.
Bláthíne f Irish Mythology
Variant of Bláthnat using a different diminutive suffix, used in some versions of the legend.
Bláthnaid f Irish, Irish Mythology
Modern Irish form of Bláthnat.
Bláthnat f Irish Mythology
Means "little flower" from Irish bláth "flower" combined with a diminutive suffix. In Irish legend she was a maiden abducted and married by Cú Roí. She was rescued by Cúchulainn, who killed her husband, but was in turn murdered by one of Cú Roí's loyal servants.
Boann f Irish Mythology
Possibly from Old Irish "cow" and finn "white, blessed". In Irish mythology this was the name of the goddess of the River Boyne, which is named for her. She was the wife of Nechtan and the father of Aonghus (by Dagda).
Bóinn f Irish Mythology
Modern Irish form of Boann.
Bran 1 m Irish, Irish Mythology, Old Irish
Means "raven" in Irish. In Irish legend Bran mac Febail was a mariner who was involved in several adventures on his quest to find the Otherworld.
Brígh f Irish Mythology
From Old Irish bríg meaning "might, power". This was the name of a daughter of the Irish god Dagda.
Brighid f Irish, Irish Mythology
Newer Irish form of Brigit (see Bridget). Since the 1948 spelling reform, this name is spelled Bríd.
Brigid f Irish, Irish Mythology
Irish variant of Brighid (see Bridget).
Cáel m Irish Mythology
From Old Irish cáel meaning "slender". In Irish legend Cáel was a warrior of the Fianna and the lover of Créd.
Céibhfhionn f Irish Mythology
Means "fair-haired", from Old Irish ciab "locks, hair" and finn "white, blessed". In Irish legend this was the name of one of the three daughters of Bec mac Buain.
Cian m Irish, Irish Mythology, Old Irish
Means "ancient, enduring" in Irish. In Irish mythology this was the name of the father of Lugh Lámfada. It was also borne by the mythical ancestor of the Ciannachta and by a son-in-law of Brian Boru.
Ciar m & f Irish, Irish Mythology, Old Irish
Derived from Irish ciar meaning "black". In Irish legend Ciar was a son of Fergus mac Róich and Medb, and the ancestor of the tribe of the Ciarraige (after whom County Kerry is named). As a feminine name, it was borne by an Irish nun (also called Ciara) who established a monastery in Tipperary in the 7th century.
Cleena f Irish Mythology
Anglicized form of Clíodhna.
Clídna f Irish Mythology
Old Irish form of Clíodhna.
Clíodhna f Irish, Irish Mythology
Meaning unknown. In Irish legend this was the name of a beautiful goddess. She fell in love with a mortal named Ciabhán and left the Land of Promise with him, but when she arrived on the other shore she was swept to sea by a great wave.
Conall m Irish, Old Irish, Irish Mythology
Means "rule of a wolf", from Old Irish "hound, dog, wolf" (genitive con) and fal "rule". This is the name of several characters in Irish legend including the hero Conall Cernach ("Conall of the victories"), a member of the Red Branch of Ulster, who avenged Cúchulainn's death by killing Lugaid.
Conchobar m Old Irish, Irish Mythology
Derived from Old Irish "hound, dog, wolf" (genitive con) and cobar "desiring". It has been in use in Ireland for centuries and was the name of several Irish rulers. It was borne by the Ulster king Conchobar mac Nessa, one of the central characters in the Ulster Cycle of Irish mythology, known for his tragic desire for Deirdre and his war with Queen Medb of Connacht.
Conchobhar m Irish Mythology
Modern Irish form of Conchobar.
Conchúr m Irish, Irish Mythology
Modern Irish form of Conchobar.
Conn m Irish, Irish Mythology, Old Irish
Perhaps from Old Irish conn meaning "sense, reason" or cenn meaning "head, chief". This was the name of a legendary high king of Ireland, Conn of the Hundred Battles.
Connla m Irish Mythology
From Old Irish Conláech, derived from "hound, dog, wolf" (genitive con) and láech "warrior". This was the name of several characters in Irish legend including the son of Cúchulainn and Aoife. When he finally met his father they fought because Connla would not identify himself, and the son was slain.
Conor m Irish, English, Irish Mythology
Anglicized form of Conchobar (or the Modern Irish form Conchúr).
Cormac m Irish Mythology, Irish
From Old Irish Cormacc or Corbmac, of uncertain meaning, possibly from corb "chariot, wagon" or corbbad "defilement, corruption" combined with macc "son". This is the name of several characters from Irish legend, including the semi-legendary high king Cormac mac Airt who supposedly ruled in the 3rd century, during the adventures of the hero Fionn mac Cumhaill. This name was also borne by a few early saints.
Cúchulainn m Irish Mythology
Means "hound of Culann" in Irish. This was the usual name of the warrior hero who was named Sétanta at birth, given to him because he took the place of one of Culann's hounds after he accidentally killed it. The Ulster Cycle of Irish mythology tells of Cúchulainn's many adventures, including his single-handed defence of Ulster against the army of Queen Medb.
Culann m Irish Mythology
Meaning unknown. This was the name of a smith in Irish legend. After Sétanta killed one of his dogs in self-defence, Sétanta took the place of the dog and was thereafter known as Cúchulainn.
Dagda m Irish Mythology
Means "the good god" from the Old Irish prefix dag- "good" and día "god". In Irish myth Dagda (called also The Dagda) was the powerful god of the earth, knowledge, magic, abundance and treaties, a leader of the Tuatha Dé Danann. He was skilled in combat and healing and possessed a huge club, the handle of which could revive the dead.
Dáire m Irish, Irish Mythology
Means "fruitful, fertile" in Irish. This name is borne by many figures in Irish legend, including the Ulster chief Dáire mac Fiachna who reneged on his promise to loan the Brown Bull of Cooley to Medb, starting the war between Connacht and Ulster as told in the Irish epic The Cattle Raid of Cooley.
Dáirine f Irish, Irish Mythology
Possibly derived from Dáire. This was the name of the daughter of the legendary Irish king Túathal Techtmar.
Deimne m Irish Mythology
Means "sureness, certainty" in Irish. This was the birth name of the Irish hero Fionn mac Cumhaill.
Deirdre f English, Irish, Irish Mythology
From the Old Irish name Derdriu, meaning unknown, possibly derived from der meaning "daughter". This was the name of a tragic character in Irish legend who died of a broken heart after Conchobar, the king of Ulster, forced her to be his bride and killed her lover Naoise.... [more]
Diarmaid m Irish, Irish Mythology
Meaning unknown, though it has been suggested that it means "without envy" in Irish. In Irish legend this was the name of a warrior who became the lover of Gráinne. It was also the name of several ancient Irish kings.
Doireann f Irish, Irish Mythology
Possibly from the Old Irish prefix der "daughter" and finn "white, blessed". Alternatively it may be derived from Irish doireann "sullen, tempestuous". This was the name of several characters in Irish legend, including a daughter of Bodb Derg who poisoned Fionn mac Cumhaill after he spurned her advances.
Eadán f Irish Mythology
Modern Irish form of Étan.
Éadaoin f Irish, Irish Mythology
Modern Irish form of Étaín.
Éber m Irish Mythology
Old Irish form of Éibhear.
Éibhear m Irish Mythology
From Old Irish Éber, meaning uncertain. According to Irish legend this name belonged to two of the sons of Míl, Éibhear Dunn and Éibhear Finn, the first of the Gaels to conquer Ireland.
Éimhear f Irish, Irish Mythology
Modern Irish form of Emer.
Eithne f Irish, Irish Mythology, Old Irish
Possibly from Old Irish etne meaning "kernel, grain". In Irish mythology Eithne or Ethniu was a Fomorian and the mother of Lugh Lámfada. It was borne by several other legendary and historical figures, including a few early saints.
Emer f Irish Mythology
Meaning unknown. In Irish legend she was the wife of Cúchulainn. She was said to possess the six gifts of womanhood: beauty, voice, speech, needlework, wisdom and chastity.
Eógan m Old Irish, Irish Mythology
Old Irish form of Eoghan.
Eoghan m Irish, Irish Mythology
Possibly means "born from the yew tree", from Old Irish "yew" and the suffix gan "born". Alternatively, it might be derived from the Latin name Eugenius. It was borne by several legendary or semi-legendary Irish figures, including a son of the king Niall of the Nine Hostages.
Ériu f Irish Mythology
From the name of an Irish goddess, who according to legend gave her name to Ireland (which is called Éire in Irish). In reality, the goddess probably got her name from that of the island, which may mean something like "abundant land" in Old Irish.
Étaín f Irish, Irish Mythology, Old Irish
Possibly derived from Old Irish ét meaning "jealousy, passion". In Irish legend she is the subject of the 9th-century tale The Wooing of Étaín. She was the wife of Midir, but his jealous first wife Fuamnach transformed her into a fly. She was accidentally swallowed, and then reborn to the woman who swallowed her. After she grew again to adulthood she married the Irish high king Eochaid Airem, having no memory of Midir. Midir and Étaín were eventually reunited after Midir defeated Eochaid in a game of chess.... [more]
Étan f Irish Mythology
Possibly a variant of Étaín. In Irish mythology she was the daughter of Dian Cécht, the god of healing.
Fachtna m Irish, Old Irish, Irish Mythology
Possibly from Old Irish facht meaning "malice". This was the name of a legendary high king of Ireland, said in some traditions to be the husband of Neasa and the father of Conchobar.
Fearghas m Irish, Scottish Gaelic, Irish Mythology
Irish and Scottish Gaelic form of Fergus.
Fedelm f Irish Mythology, Old Irish
Possibly a feminine form of Feidlimid. This name is borne by several women in Irish legend including Fedelm Noíchrothach, a daughter of Conchobar the king of Ulster. It was also the name of a few early saints.
Feidlimid m & f Old Irish, Irish Mythology
Traditionally said to mean "ever good", it might be related to Old Irish feidil "enduring, constant". This was the name of three early kings of Munster. It was also borne by a 6th-century saint, typically called Saint Felim. In Irish legend, it was the name of the father of Deirdre.
Fergus m Irish, Scottish, Irish Mythology, Old Irish
Means "man of vigour", derived from the Old Irish elements fer "man" and guss "vigour, strength, force". This was the name of several early rulers of Ireland and Dál Riata, as well as many characters from Irish legend. Notably it was borne by the hero Fergus mac Róich, who was tricked into giving up the kingship of Ulster to Conchobar. However, he remained loyal to the new king until Conchobar betrayed Deirdre and Naoise, at which point he defected to Connacht in anger. The name was also borne by an 8th-century saint, a missionary to Scotland.... [more]
Fiachna m Irish Mythology, Old Irish
Derived from Irish fiach meaning "raven". This is the name of several characters from Irish legend. It was also borne by Fiachna mac Báetáin, a 7th-century king of Dál Araide.
Fiachra m Irish, Irish Mythology
From Old Irish Fiachrae, possibly from fiach "raven" or fích "battle" combined with "king". This was the name of several legendary figures, including one of the four children of Lir transformed into swans for a period of 900 years. This is also the name of the patron saint of gardeners: a 7th-century Irish abbot who settled in France, usually called Saint Fiacre.
Finn 1 m Irish Mythology, Old Irish, Irish, English, Dutch, German
Old Irish form of Fionn, as well as the usual Anglicized spelling (with the Irish hero's name Anglicized as Finn McCool). As a surname it is borne by Huckleberry Finn, a character in Mark Twain's novels.
Fintan m Irish, Irish Mythology, Old Irish
Possibly means either "white fire" or "white ancient" in Irish. According to legend this was the name of the only Irish person to survive the great flood. This name was also borne by many Irish saints.
Fionn m Irish, Irish Mythology
From the Old Irish name Finn, derived from finn meaning "white, blessed". It occurs frequently in Irish history and legends, the most noteworthy bearer being Fionn mac Cumhaill, the central character of one of the four main cycles of Irish mythology, the Fenian Cycle. Fionn was born as Deimne, and acquired his nickname because of his fair hair. He grew all-wise by eating an enchanted salmon, and later became the leader of the Fianna after defeating the fire-breathing demon Áillen. He was the father of Oisín and grandfather of Oscar.
Fionnuala f Irish, Irish Mythology
Means "white shoulder" from Old Irish finn "white, blessed" and gúala "shoulder". In Irish legend Fionnuala was one of the four children of Lir who were transformed into swans for a period of 900 years.
Goibniu m Irish Mythology
Derived from Old Irish gobae meaning "smith". In Irish mythology this was the name of a divine metalsmith and weapon maker of the Tuatha Dé Danann. He also provided them with feasts that protected them from old age. He may be derived from an earlier Celtic smith god (seen also in Gaulish Gobannos and Welsh Gofannon).
Gráinne f Irish, Irish Mythology, Old Irish
Possibly derived from Old Irish grán meaning "grain" or gráin meaning "hatred, fear". In the Irish legend The Pursuit of Diarmaid and Gráinne she escaped from her arranged marriage to Fionn mac Cumhaill by fleeing with her lover Diarmaid. Another famous bearer was the powerful 16th-century Irish landowner and seafarer Gráinne Ní Mháille (known in English as Grace O'Malley), who was sometimes portrayed as a pirate queen in later tales.
Heber 1 m Irish Mythology
Anglicized form of Éibhear.
Ler m Irish Mythology
Means "the sea" in Old Irish. Ler was probably an Irish god or personification of the sea, best known as the father of Manannán mac Lir.
Lir m Irish Mythology
Possibly from the patronymic Manannán mac Lir, in which case Lir is the genitive case of the name Ler. The medieval Irish legend the Children of Lir tells how Lir of the Tuatha Dé Danann had his children transformed into swans by his third wife Aoife. The legendary characters Lir and Ler seem to be distinct.
Lóegaire m Irish Mythology, Old Irish
Means "calf herder", derived from Old Irish lóeg "calf". In Irish legend Lóegaire Búadach was an Ulster warrior. He saved the life of the poet Áed, but died in the process. This was also the name of several Irish high kings.
m Irish Mythology
Modern Irish form of Lugh.
Lug m Irish Mythology
Old Irish form of Lugh.
Lugh m Irish Mythology
Probably an Irish form of Lugus. In Irish mythology Lugh Lámfada was a divine hero who led the Tuatha Dé Danann against his grandfather Balor and the Fomorians. Lugh killed Balor by shooting a stone into his giant eye.
Lughaidh m Irish Mythology
From Old Irish Lugaid, a combination of the name of the mythological figure Lugh and Old Irish dech "honour, better". This was the name of several characters in Irish legend, including the king Lugaid mac Con.
Maeve f Irish, English, Irish Mythology
Anglicized form of the Irish name Medb meaning "intoxicating". In Irish legend this was the name of a warrior queen of Connacht. She and her husband Ailill fought against the Ulster king Conchobar and the hero Cúchulainn, as told in the Irish epic The Cattle Raid of Cooley.
Manannán m Irish Mythology
Probably from the name of the Isle of Man, itself possibly from the Celtic root *moniyo- meaning "mountain". In Irish mythology Manannán mac Lir was a god of the sea and one of the Tuatha Dé Danann.
Méabh f Irish, Irish Mythology
Modern Irish form of Medb (see Maeve).
Meadhbh f Irish, Irish Mythology
Modern Irish form of Medb (see Maeve).
Medb f Irish Mythology
Original Irish form of Maeve.
Morrígan f Irish Mythology
Means either "demon queen" or "great queen", derived from Old Irish mor "demon, evil spirit" or mór "great, big" combined with rígain "queen". In Irish mythology Morrígan (called also The Morrígan) was a goddess of war and death who often took the form of a crow.
Muirenn f Old Irish, Irish Mythology
From Old Irish muir "sea" and finn "white, blessed". This is another name of Muirne, the mother of the legendary hero Fionn mac Cumhaill.
Muirgen f Irish Mythology
Means "born of the sea" in Irish. In Irish legend this was the name of a woman (originally named Lí Ban) who was transformed into a mermaid. After 300 years she was brought to shore, baptized, and transformed back into a woman.
Muirne f Irish Mythology
From Irish muirn meaning either "affection, endearment" or "festivity, exuberance". In Irish legend this was the name of the mother of Fionn mac Cumhaill. She is also called Muirenn.
Naoise m Irish, Irish Mythology
Meaning unknown, presumably of Irish origin. In Irish legend he was the young man who fled to Scotland with Deirdre, who was due to marry Conchobar the king of Ulster. Conchobar eventually succeeded in capturing Deirdre and killing Naoise, which caused Deirdre to die of grief.
Neas f Irish Mythology
Old Irish form of Neasa.
Neasa f Irish, Irish Mythology
From Old Irish Ness, meaning uncertain. In Irish legend she was the mother of Conchobar. She installed her son as king of Ulster by convincing Fergus mac Róich (her husband and Conchobar's stepfather) to give up his throne to the boy for a year and then helping him rule so astutely that the Ulstermen demanded that he remain as king. According to some versions of the legend she was originally named Assa "gentle", but was renamed Ní-assa "not gentle" after she sought to avenge the murders of her foster fathers.
Nechtan m Irish Mythology, Old Irish
Irish name of uncertain meaning, possibly from a Celtic root meaning "damp" (cognate with Neptune). In Irish mythology Nechtan was the husband of Boann, the goddess of the River Boyne. He is sometimes identified with Nuada. This name was borne by the 5th-century Saint Nectan of Hartland in Devon, who was supposedly born in Ireland. It was also the name of several kings of the Picts (described mostly from Gaelic sources, this may represent a Pictish cognate).
Ness 1 f Irish Mythology
Old Irish form of Neasa.
Nessa 3 f Irish, Irish Mythology
Anglicized form of Neasa.
Níam f Irish Mythology
Old Irish form of Niamh.
Niamh f Irish, Irish Mythology
Means "bright" in Irish. She was the daughter of the sea god Manannán mac Lir in Irish legends. She fell in love with the poet Oisín, the son of Fionn mac Cumhaill. It has been used as a given name for people only since the early 20th century.
Noíse m Irish Mythology
Old Irish form of Naoise.
Nuada m Irish Mythology
From Old Irish Nuadu, probably from Nodens. In Irish mythology he was the first king of the Tuatha Dé Danann. After he lost an arm in battle it was replaced with one made from silver, and he received the byname Airgetlám meaning "silver hand". He was later killed fighting the monstrous Fomorians led by Balor. This name was also borne by a few semi-legendary Irish kings.
Nuadha m Irish Mythology
Modern Irish form of Nuada.
Nuadu m Irish Mythology, Old Irish
Old Irish form of Nuada.
Oisín m Irish, Irish Mythology
Means "little deer", derived from Old Irish oss "deer, stag" combined with a diminutive suffix. In Irish legend Oisín was a warrior hero and a poet, the son of Fionn mac Cumhaill and the narrator in many of his tales.
Oscar m English, Irish, Portuguese (Brazilian), Italian, Swedish, Norwegian, Danish, Dutch, French, Irish Mythology
Possibly means "deer friend", derived from Old Irish oss "deer" and carae "friend". Alternatively, it may derive from the Old English name Osgar or its Old Norse cognate Ásgeirr, which may have been brought to Ireland by Viking invaders and settlers. In Irish legend Oscar was the son of the poet Oisín and the grandson of the hero Fionn mac Cumhaill.... [more]
Parthalán m Irish Mythology
Modern Irish form of Partholón.
Partholón m Irish Mythology
Probably from the Biblical Latin name Bartholomeus (see Bartholomew). According to the 11th-century Irish history the Book of Invasions, he was the leader of the first group of settlers to arrive on Ireland after the biblical flood, though they soon all died of disease. Earlier, he briefly appears in the form Partholomus in the 9th-century History of the Britons, written in Latin.
Ríoghnach f Irish Mythology
Derived from Old Irish rígain meaning "queen". According to some sources, this was the name of a wife of the semi-legendary Irish king Niall of the Nine Hostages.
Sabia f Irish Mythology
Latinized form of Sadb.
Sadb f Irish Mythology, Old Irish
Probably derived from the old Celtic root *swādu- meaning "sweet". This was a common name in medieval Ireland. In Irish mythology Sadb was a woman transformed into a deer. She was the mother of Oisín by Fionn mac Cumhaill.
Sadhbh f Irish, Irish Mythology
Modern Irish form of Sadb.
Saraid f Irish, Irish Mythology
From Old Irish Sárait, derived from sár meaning "excellent". This was the name of a daughter of the legendary high king of Ireland, Conn of the Hundred Battles.
Sárait f Irish Mythology
Old Irish form of Saraid.
Scáthach f Irish Mythology
Means "shadowy" in Irish. In Irish legend this was the name of a warrior woman. She instructed Cúchulainn in the arts of war, and he in turn helped her defeat her rival Aoife.
Sionann f Irish Mythology
In Irish legend this was the name of a granddaughter of the sea god Lir who went to Connla's Well, which was forbidden. The well burst and drowned her, leaving her body in the river thereafter known as the Sionainn (see Shannon).
Sláine f & m Old Irish, Irish Mythology
From Old Irish slán meaning "health, safety". This was the name of a legendary high king of Ireland, one of the Fir Bolg. It was also the name of a daughter of the 11th-century high king Brian Boru.
Suibhne m Irish Mythology
From Old Irish Suibne, possibly derived from subae meaning "joy, pleasure". This was the name of several figures from early Irish history, including a 7th-century high king and an 8th-century saint. It also appears in the Irish legend Buile Suibhne (meaning "The Madness of Suibhne") about a king who goes insane after being cursed by Saint Rónán Finn.
Sweeney m Irish Mythology
Anglicized form of Suibhne. In fiction, this name is borne by the murderous barber Sweeney Todd, first appearing in the British serial The String of Pearls: A Romance (1846-1847).
Tadg m Old Irish, Irish Mythology
Old Irish form of Tadhg.
Tadhg m Irish, Irish Mythology
From Old Irish Tadg meaning "poet". This was the name of an 11th-century king of Connacht, as well as several other kings and chieftains of medieval Ireland. According to Irish mythology it was the name of the grandfather of Fionn mac Cumhaill.