Mael Duin, son of Ailill, "Edge of Battle," of the sept of the Eoghanachta of Aran, was born after his father had raped a nun. The nun died in childbirth and Ailill went on to meet his own death at the hands of raiders from overseas. The boy was fostered by the nun's sister, who eventually tells him the story of his birth. Mael Duin then sets out in a quest to avenge his father's death. He takes sixry warriors with him, and his subsequent voyage and adventures have been considered the "Irish Odyssey."

Mael Fhothartaig. [I] Son of Ronin of leinster who rejected his stepmother's advances but was falsely accused by her. His father, believing his wife, had his son slain. Mael Fhothartaigis sons later avenged him.

Maen Tyriawc. [W] The burial place of Pryderi, lord of Dyfed.

Maer. [I] A married woman, she fell in love with Fionn Mac Cumhail and sent him nine charm nuts to make him reciprocate her sentiments. Suspecting their purpose, Fionn refused to eat them.

Maga. [I] Daughter of the love god Aonghus Og, she wed Ross the Red, and their son Fachtna wed Nessa, the mother of Conchobhar Mac Nessa.

Magh. [I] Sometimes Anglicised as Mag or Moy, the word indicates a plain. Plains frequently occur in the myths and sagas as euphemism for the Otherworld: for example, Magh Da Cheo (Plain of the Two Mists), Magh Mell (The Pleasant Plain), and others.

Magh Indoc. [I] The Plain of Indoc features in a Christian embellishment to the myths in which Cuchulainn appears when St. Patrick is walking with Laoghaire Mac Neill (High King A.D. 428-463) on the plain. Cuchulainn appeals to laoghaire to be converted to Christianity and asks St. Patrick to intercede so that he might be released from Hell and go to the Christian Heaven.

Magh Slecht. [I] Sometimes given as Moyslaught. The Plain of Adoration, said to be located in north Co. Cavan, where the idol Crom Cruach was erected.

Magh Tuireadh. [I] Sometimes given as Moytura. The Plain of Towers. This is the site of two famous battles in mythology. The first battle was fought when the De Danaan led by Nuada clashed with the Firbolgs led by Erc. The De Danaan won but Nuada's hand was struck off and the god of medicine, Dian cecht, replaced it with a silver one. The second battle was between the De Danaan and the Fomorii. Nuada was slain in this battle by Balor of the Evil Eye, who was in turn slain by Lugh Lamhfada. Maine. [I] There are several people called Maine in Irish myth, but they are usually minor characters. The seven sons of Ailill and Medb of Connacht are all called Maine. The most prominent, however, is a Norse prince who, in one version of the tragic tale of Deirdre and the sons of Usna, is the person who kills Naoise and his brothers.

Manannan Beg/Mac y Leirr. Manx equivalent of Manannin Mac Lir/Manawydan Fab Llyr .

Manannan Mac Lir. [I] The major sea god, son of Lir. He ruled from Emain Ablach (Emain of the Apple Trees) in Tir Tairnigiri (Land of Promise) .His wife was Fand, the Pearl of Beauty. His appearance is always as a noble and handsome warrior, but he is a shape-changer and can drive his chariot over the waves as if they were a plain. Although he sired children among the gods, such as Gaiar, whose affair with Becuma caused her expulsion from the Land of Promise, Manannin also sired human children like Mongin. In one version of Mongin's begetting, Manannin is said to have appeared to Fachtna, the king, who was loosing in a battle, and offered to help him if he could go, disguised as Fachtna, and sleep with his wife. To this Fachtna agrees. The child of this union became a great king and mighty warrior. This tale is remarkably similar to that of the conception and birth of Arthur in Btythonic Celtic myth. Manannin appears more frequently than most gods, creating storms or wrecking Milesian ships, appearing to Bran at the start of his epic voyage, and conducting Cormac Mac Art around Tir Tairnigiri. When the Dagda resigns the leadership of the gods, it is Manannin who refuses to accept the succession of the Bodb Dearg and retreats into seclusion.

Manawydan Cab Llyr. [W] See Manannan Mac Lir. Manawydan, son of Llyr, the counterpart of the Irish sea god Manannin, son of Lir, forms a close though not exact parallel. However, we can assume that they were a single deity known and venerated among both linguistic Celtic groupings. In the Third Branch of the Mabinogion, Manawydan is represented as a wise and patient counsellor, but there is no indication that he is thought of as the god of the sea. It seems that the traditions had been reshaped at a later date, with Manawydan changed into a mortal rather than an immortal. There was a similar tendency in Ireland, to appease the sensibilities of the Christian scribes, to change the status of the ancient gods. There are close parallels in the tales of Bran of Ireland and Bran ofWales, in which Manannan and Manawydan feature. Manawydan is depicted as brother of Benedigeid Vran, or Bran the Blessed, king of the Isle of the Mighty (Britain).
In the story of Pryderi and Manawydan, Manawydan appears as the husband of Rhiannon. Manawydan and Rhiannon, with Pryderi and his wife, Cigva, are living at their palace at Arbeth, in the kingdom of Dyfed, when a peal of thunder is heard and a mist falls. When it clears, the land is desolate. None of the people remain except the four of them. There are no cattle herds nor crops. After two years, existing on wild honey and what little they could kill, they decided to seek their fortune in Lloegyr (England). After several adventures, Pryderi, despite the wise counsel of Manawydan, follows a magic boar into a castle where he finds a fountain with a golden bowl on a marble slab. (See Cauldron. Magic. and Grail). He tries to take hold of it, is struck dumb, and is unable to let go. Manawydan tells Rhiannon, who tries to rescue him but suffers a similar fate. A mist causes them to disappear . Manawydan and Cigva have more adventures until an encounter with Llwyd, son of Cilcoed, who reveals that all the enchanted happenings have been placed on Dyfed by him as an act of revenge for his friend, Gwawal, son of Clud, whom Pryderi's father and warriors had ill-used. Thus the tale takes us back to the story of Rhiannon's wedding in the first Mabinogi. Pryderi and Rhiannon are released from the spell, as are all the people and animals of Dyfed.