great-great-grandfather
Refers to the grandfather of one's grandparent. A formal kinship term; in casual conversation, people may simply say ひいひいおじいさん.
My great-great-grandfather was born in the Meiji era.
Compound of 高 (great, high) and 祖父 (grandfather). The prefix 高 indicates a generation beyond 曽祖父 (great-grandfather).