A more thorough explanation:

Proavunculus (proh-uh-vuhngk-yuh-luhs) is a legal term that comes from Latin. It refers to a great-grandmother's brother.

For example, if your great-grandmother had a brother, he would be your proavunculus. Even though this term is not commonly used today, it was important in Roman law for determining inheritance and family relationships.

Another example would be if you were researching your family tree and discovered that your great-grandmother had a brother. You could use the term proavunculus to describe your relationship to him.

The term proavunculus is very specific and refers only to a great-grandmother's brother. It is important in legal contexts, such as inheritance, because it helps to establish family relationships and determine who is entitled to certain rights or property. While this term may not be commonly used today, it is still relevant in some legal systems and can be helpful in genealogical research.