Matholwch. [W] King of Ireland who marries Branwen, daughter of Llyr. He is slighted by her half-brother Efnisien and in revenge mistreats Branwen, forcing her to do menial tasks in his kitchens despite the birth of their son Gwern. This leads to an invasion of Ireland by Bran, Branwen's brother, and a destructive battle in which Matholwch is killed. Only five pregnant women are left alive in all Ireland to repopulate the country .

Mathonwy. [W] Ancestor of the house of Don. His children were Don, the mother-goddess, and Math, god of increasing wealth. Matrona. Divine Mother, a Gaulish goddess. See Mabon.

Meargach. [I] "Of the Green Spears." Husband of Aille who is killed by Oscar .

Mechi. [I] Son of the M6rrigan, goddess of death and battles, who is slain by Mac cecht, son of Ogma, because it is prophesied that he will bring disaster to Ireland. He had three hearts in which grew three serpents that, when full grown, would break out and devastate the land.

Medb. [I] Sometimes Anglicised as Maeve. It has been argued that she was another triune goddess representing sovranty. She is most famous for her appearance in the epic of the Tain Bo Cuailgne.

Meddygon Meddfai. [W] Three sons of a mortal and an Otherworld spirit who, through her knowledge, became the greatest physicians in Wales. See Llyn y Fan.

Medicine. Much is made of the skills of ancient Celtic physicians, especially the Irish. During the Dark Ages (the Golden Age of Learning for Ireland) the Irish medical schools were famous throughout Europe. The premier medical school of Europe was at Tuaim Brecain (Tomregan, Co. Cavan) in the fifth century A.D. Both the Brehon Laws and the Laws of Hywel Dda are very explicit on medical practices. The oldest surviving medica}. books in Irish date from the eatly fourteenth century and constitute the largeSt collection of medical manuscript literature, prior to 1800, surviving in anyone language.
Dian cecht was the main Irish god of medicine, but he became , jealous of the abilities of his children, such as Miach, who gave Nuada a flesh and blood hand while he could only give him one of silver. The Book of the O'Lees, written in 1443, is written in forms resembling the pattern of astrological figures. It is said that the book was given to O'Lee by Otherworld folk from Hy-Brasil. This tale is remarkably similar to the story of the Meddygon Meddfai, who are also given an Otherworld book of medical knowledge and become ': the greatest physicians in Wales.

Medrawd. [W] See Melwas.

Meilge. [I] A High King who slew Aige when in the form of a deer Her brother Fafne composed a satire about him that caused a blemish to form three blotches on his face. For this Fafne was put to death.

Melwas. [W] King of the Summer Land, Somerset, who kidnaps Arthur's queen Gwenhwyfar. Gildas intervenes and persuades him to return the queen. He appears as Meleagant in Le Chavalier de la Charrette by Chreuen de Troyes, and as Mellyagraunce In Malory s Morte d'rthur.

Menw. [W] A warrior who accompanies Culhwch.

Merlin. [W] A magician, or druid, who plays an important role in the Arthurian sagas. He is of distinctly Celtic origin and figures prominently in early Welsh writings. The first known fully developed treatment of him is in Libellus Merline (Little Book of Merlin), ca. A.D. 1135, a Latin tract written by GeofFrey of Monmouth, which was incorporated into his Historia. See Myrddin.

Mermaids/Mermen. As in other cultures, mermaids and mermen (muirgen = sea child) abound in the sagas and tales of Celtic myth. From Brittany to Ireland and from Scotland to Cornwall, such tales survive in folkloric tradition. Half human, half fish, they dwell in the sea. While the mermaids are always enticing and beautiful, the mermen usually have pig's eyes red noses, and green hair.   They are both benevolent and malevolent.
Cornwall is especially awash in mermaid traditions. There are tales of mermaids at Padstow, at Seaton, of the mermaid's rock off Lamorna, and of voices from the sea. Most famous of all is the story of the Zennor mermaid who fell in -love with the squire's son and spirited him away to sea. In the church at Zennorone of the bench ends has a carving of the mermaid. The story inspired the film Miranda (1947) with Glynis Johns and its sequel, Mad About Men (1955). These films were translated to America in 1988 as Splash

Mess Buachalla. [I] Daughter of Etain Gig and Cormac, king of Ulster, her father ordered her to be killed because he wanted a son. The two men who undertook the task left the child in the barn of the cowherd of the High King Eterscel. It was prophesied that a woman of an unknown race would bear a son who would be famous, so when her beauty becomes known, Eterscel plans to marry her. On the night before the wedding she is visited by Nemglan, the bird god, and the result of their union is Conaire Mor, although Mess Buachalla is wedded to the High King, who brings him up as his own child.

Miach. [I] A son of Dian cecht, god of medicine, who proved a better physician than his father, who grew jealous at his accomplishments and murdered him. Herbs grew from his grave that were gathered by his sister Airmid, who laid them out on a cloak in order of their curative values. But her father shook the cloak and so jumbled them that their secrets vanished forever .

Mide. [I] Eponym of Meath, the Middle Province. In the days of the Ulster cycle, Ireland consisted of only four provinces. The fifth province, Mide, was established by the High King Tuathal Teachmhair, A.D. 130-160, so that the High Kings might be independent of the politics of the four provinces. Hence the term "Royal Meath," which still survives.

Midir the Proud. [I] Son of the Dagda and a powerful god himself. He dwelt at the sidhe of Bri Leith, Slieve Calloty, west of Ardagh, Co. Longford. When the Dagda resigned the leadership of the gods, . he refused to accept the choice of the Bodb Dearg and made war on him. This "civil war" among the gods seemed inconclusive, but it meant the end of the power of the gods and they retreated into their underground palaces and became fairies in the minds of the people.