| Welsh baby names begining from M |
| Mabli |
 | Welsh form of Mabel, meaning lovable. |
| Mabon |
 | Legendary son of Modron. |
| Mabsant |
 | Legendary son of Caw. |
| Madawc |
 | Beneficent. |
| Madawg |
 | Legendary son of Teithyon. |
| Maddoc |
 | Beneficent. |
| Maddock |
 | Beneficent. |
| Maddockson |
 | Son of Maddock. |
| Maddocson |
 | Son of Maddock. |
| Maddog |
 | Beneficent. |
| Maddox |
 | Son of Maddock. |
| Madoc |
 | Fortunate. Beneficent. |
| Madog |
 | Beneficent. |
| Maegan |
 | Variant of Margaret - pearl - based on the abbreviation Meg. |
| Mael |
 | Legendary son of Roycol. |
| Maelgwyn |
 | Prince of the hounds. |
| Maelwys |
 | Legendary son of Baeddan. |
| Mair |
 | Bitter. |
| Mali |
 | Welsh form of Molly: bitter. |
| Mallolwch |
 | Legendary king of Ireland. |
| Manawydan |
 | Legendary son of LIyr. |
| March |
 | Legendary son of Meirchywn. |
| Maredud |
 | Magnificent. |
| Marged |
 | Pearl. |
| Margred |
 | Pearl. |
| Mari |
 | Variant of Mary, meaning bitter. Favored prefix for blended names like Maribel. |
| Marvin |
 | Variant of Mervyn: Form of Merlin: From the sea fortress. |
| Marvyn |
 | Variant of Mervyn: Form of Merlin: From the sea fortress. |
| Mathias |
 | Gift of God. |
| Mawrth |
 | Welsh form of Mars, god of war. |
| Maygan |
 | Variant of Margaret - pearl - based on the abbreviation Meg. |
| Meagan |
 | Variant of Margaret - pearl - based on the abbreviation Meg. |
| Meaghan |
 | Variant of Margaret - pearl - based on the abbreviation Meg. |
| Medyr |
 | Legendary son of Medyredydd. |
| Meeghan |
 | Variant of Margaret - pearl - based on the abbreviation Meg. |
| Meggan |
 | Variant of Margaret - pearl - based on the abbreviation Meg. |
| Meghan |
 | Pearl. |
| Meilyg |
 | Legendary son of Caw. |
| Meirion |
 | Name derived from the old county of Merionethshire. |
| Menw |
 | Legendary son of Teinkaedd. |
| Mercher |
 | Welsh form of Mercury, messenger of the gods. |
| Mercia |
 | From Mercia. |
| Meredith |
 | Guardian of the sea. Great chief. This name can be given to children of either gender, but is more common among girls. |
| Meredith |
 | Magnificent. Great chief. Great lady. This name can be given to children of either gender, but is more common among girls. |
| Meredydd |
 | Guardian of the sea. |
| Meredydd |
 | Magnificent. |
| Mererid |
 | Pearl. |
| Meridith |
 | Guardian of the sea. |
| Merlin |
 | Hawk. From the sea fortress. In Arthurian legend, Merlin Ambrosius was adviser/mentor to King Arthur. |
| Merlyn |
 | Sea fortress. In Arthurian mythology the wizard Merlin was King Arthur's mentor. |
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