McMahon, also spelt MacMahon (older Irish orthography: Mac Mathghamhna; reformed Irish orthography: Mac Mathúna), were different Middle Age era Irish clans. Their name is derived from the Gaelic Mac Mathghamhna meaning 'son of the bear'.[1] According to historian C. Thomas Cairney, the MacMahons were one of the chiefly families of the Dal gCais or Dalcassians who were a tribe of the Erainn who were the second wave of Celts to settle in Ireland between about 500 and 100 BC.[2]