| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 521 | Linette | Celtic | Grace. | F | |
| 522 | Linnette | Celtic | Grace. | F | |
| 523 | Lir | Celtic | A mythical king. | M | |
| 524 | Llewelyn | Celtic | Ruler. | M | |
| 525 | Lloyd | Celtic | Gray. | M | |
| 526 | Llyr | Celtic | A mythical king. | M | |
| 527 | Luxovious | Celtic | Mythical god of Luxeuil. | M | |
| 528 | Lynet | Celtic | Grace. | F | |
| 529 | Lynette | Celtic | Grace. | F | |
| 530 | Lyonesse | Celtic | Little lion. | F | |
| 531 | Mabina | Celtic | Nimble. | F | |
| 532 | Mabon | Celtic | Mythical god of youth. | M | |
| 533 | Mac | Celtic | Son of. | M | |
| 534 | Maccus | Celtic | Hammer. | M | |
| 535 | Mack | Celtic | Son of. | M | |
| 536 | Macklin | Celtic | Son of Flann. | M | |
| 537 | Macklyn | Celtic | Son of Flann. | M | |
| 538 | Maddock | Celtic | Beneficent. | M | |
| 539 | Maddox | Celtic | Beneficent. | M | |
| 540 | Maeve | Celtic | A mythical queen. | F | |