The Irish surname McMahan is an anglicized form of Gaelic Mac Mathghamhna, a patronymic from the byname Mathghamhain meaning “good calf.” This was the name of two (unrelated) chieftain families in counties Clare and Monaghan. The most outstanding McMahan /McMahon was Edmond Patrice, Compte de MacMahon (1808 - 1893), Marshal of France, and President of the Third Republic for six years. The family Coat of Arms is a silver shield with three red lions passant reguardant in pale, armed and langued azure.