| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 341 | Leigh | Celtic | Healer. | M | |
| 342 | Leith | Celtic | Meadow. | M | |
| 343 | Lesley | Celtic | From the gray fortress. | M | |
| 344 | Leslie | Celtic | From the gray fortress. | M | |
| 345 | Lincoln | Celtic | From the settlement by the pool. | M | |
| 346 | Lir | Celtic | A mythical king. | M | |
| 347 | Llewelyn | Celtic | Ruler. | M | |
| 348 | Lloyd | Celtic | Gray. | M | |
| 349 | Llyr | Celtic | A mythical king. | M | |
| 350 | Luxovious | Celtic | Mythical god of Luxeuil. | M | |
| 351 | Mabon | Celtic | Mythical god of youth. | M | |
| 352 | Mac | Celtic | Son of. | M | |
| 353 | Maccus | Celtic | Hammer. | M | |
| 354 | Mack | Celtic | Son of. | M | |
| 355 | Macklin | Celtic | Son of Flann. | M | |
| 356 | Macklyn | Celtic | Son of Flann. | M | |
| 357 | Maddock | Celtic | Beneficent. | M | |
| 358 | Maddox | Celtic | Beneficent. | M | |
| 359 | Malcolm | Celtic | Servant of Saint Columba. | M | |
| 360 | Malvin | Celtic | Leader. | M | |