Great grandfather is a term used to describe someone's grandfather's father, however, there are several synonyms that can also be used to describe this relationship. One of the most common is "grandfather's grandfather," which directly refers to the person's immediate lineage. Alternatively, one could also refer to this individual as an "ancestral grandfather" or "forefather." Another option might be to use a more generic term like "ancestor" or "progenitor," which doesn't necessarily identify the specific relationship, but still acknowledges the importance of the individual's role in the family's history. Ultimately, though, the exact terminology used may vary depending on cultural or regional traditions.