Wiktionary
great-grandpa
n. A great-grandfather.
Usage examples of "great-grandpa".
My great-grandpa was one of Dearborn's riflemen at the second battle of Saratoga, and Grandpa sailed the seas with Decatur and Bainbridge.
Great-grandpa Ralph writes in his journal that he discovered the Wankie coal field but Rhodes cheated him out of it.