
"...This Irish surname of MIMNAGH is the Anglicized form of the Gaelic O'MUIMHNEACHAIN, and is occasionally used as a synomyn of the names MINNOGUE, MINNAGH and MOYNIHAN.
There was a sept of some importance of the Hy Fiachrach called O'MIONACHAIN, dating back to the year 1220. The name means 'a Munsterman'.
The earliest of the name on record appears to be The Bishop of Leighlin who died in 1050, Clerichen O'MUINEOC, who was described in the Annals of Loch Ce as 'tower of the piety of Erin'. Ireland is one of the earliest sources of the development of patronymic names in northern Europe..." (as found on http://www.4crests.com/mimnagh-coat-of-arms.html)
Will have to look deeper into this...stay tuned for updates...

