Wiktionary
great-grandparent
n. A parent of a grandparent.
Usage examples of "great-grandparent".
And to think, he did not know the full names of his own great-grandparents or where they had been born.
His family—from tintypes of his great-grandparents who'd never stepped off Scottish soil, to snapshots of his brother and sister.
My great-grandparents went through a lot, really a lot, so they could get out of horrible places in the Balkans and come to better places in Pennsylvania and West Virginia so people like you could spend their spare time looking down their noses at them.