こうそふ
great-great-grandfather
Noun
父ちちの父ちちは祖父そふ、祖父そふの父ちちは曽祖父そふ、曽祖父そふの父ちちは高祖父こうそふだが、高祖父こうそふより前まえの世代せだいの呼称こしょうは決きまっていない。
The father of a father is a grandfather, a grandfather's father is a great-grandfather, a great-grandfather's father is a great-great-grandfather, but no word has been decided upon for the generations before great-great-grandfather.