Grandparent

Grandparent was a name used to describe one's ancestor, namely the parent of one's parent, where the subject in question would be the grandparent's grandchild. (TV: Partners in Crime) Each previous generation of the initial grandparent was given the qualifier of "great", which was then compounded. (TV: The Cambridge Spy)

The First Doctor was Susan Foreman's grandfather. (TV: "An Unearthly Child")

As the father of Sylvia Noble, Wilfred Mott was the grandfather of her daughter Donna Noble. (TV: Partners in Crime)

William Pike was the grandfather of Harry Pike, and so the great-grandfather of his son Darius Pike. (TV: The Cambridge Spy, The Last Precinct)

The term was traditionally used for the founder of a Great House. For instance, the founder of House Paradox was called "Grandfather Paradox", and the founder of House Halfling was called "Grandfather Halfling". (PROSE: The Book of the War)