A more thorough explanation:

Atmatertera

Atmatertera is a term used in civil law to refer to a great-great-great-grandmother's sister. It is also known as abmatertera magna.

If your great-great-great-grandmother had a sister, she would be your atmatertera. For instance, if you were researching your family tree and found out that your great-great-great-grandmother had a sister, you could refer to her as your atmatertera.

Another example would be if you were reading a legal document that mentioned an atmatertera. You would know that it was referring to a specific family member in the context of the document.

These examples illustrate how atmatertera is used to describe a specific relationship in civil law and genealogy.