Pet form of Margaret. Variant of Meg, The reason for the alternation of M- and P-, which occurs also in Molly/Polly, is not known; it has been ascribed to Celtic influence, but this particular alternation does not correspond to any of the usual mutational patterns in Celtic languages.
Irish: 1. Anglicized form of Gaelic Ó Miadhacháin ‘descendant of Miadhachán’, a diminutive of Miadhach, a byname meaning ‘honorable’. 2. Anglicized form of Gaelic Ó Maotháin ‘descendant of Maothán’, a personal name representing a diminutive of maoth ‘moist’, ‘soft’, ‘tearful’. 3. in some instances, an assimilated form of Mehegan.