Both great-uncle and granduncle refer to an uncle of one's father or mother.
From the en.wikipedia.org
Prince of Anhua was Zhengde's great-granduncle, while Prince of Ning was his granduncle.
From the en.wikipedia.org
Died at Wallingford, while in the custody of his granduncle, Richard, Earl of Cornwall.
From the en.wikipedia.org
His granduncle, James Blair, was founder and first president of the College of William and Mary.
From the en.wikipedia.org
The late king's elderly granduncle, Cardinal Henry, became king.
From the en.wikipedia.org
Her granduncle, Te Otinga Waretini, felt that having her stand up to talk in front of him was insulting.
From the nzherald.co.nz
Britain's Prince Charles was there with his granduncle, Lord Mountbatten, the last viceroy of India.
From the time.com
Her granduncle was the art historian Bernard Berenson.
From the time.com
Then, when Byron was 10, his granduncle died.
From the boston.com
More examples
Great-uncle: an uncle of your father or mother
In kinship terminology, a cousin is a relative with whom one shares a common ancestor (or ancestors). In modern usage, the term is rarely used when referring to a relative in one's own line of descent, or where there is a more specific term to describe the relationship: e.g. ...