The Celtic Nations with their native place names.
In legend Éire is named for the goddess Ériu, but in actuality the goddess was probably named for the island, with the name coming from Proto-Celtic Φīwerjō meaning Full/Abounding. So something like Abundant Land.
Alba ultimately comes from a proto Indo-European root meaning “White”, probably referring to the Cliffs of Dover. It originally referred to all of Britain in Goidelic, being related to the term Albion.
Kernew comes from Proto-Celtic karnos meaning “horn”, referring to the shape of the peninsula.
Mannin is named for the sea god Manannán mac Lir, or Manawydan fab Llŷr as he was called by the Welsh.
And Breizh just means “Land of the Britons”, which replaced the older Continental Celtic name of Armorica when the area was resettled by Celts from Britain in the early middle ages.