| Mona | noble good |
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| Morrisey | sea taboo |
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| Morrissey | descendant of Muiris |
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| Mulligan | descendent of the bald-headed |
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| Muriel | of the bright sea |
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| Murphy | sea warrior |
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| Myrna | festive |
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| Neve | snow |
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| Nevin | holy |
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