A more thorough explanation:

patruus magnus

Patruus magnus is a term used in Roman and civil law to refer to a great-uncle, which is the brother of one's grandfather.

• When I visited my grandmother's house, I met her brother who is my patruus magnus.
• My father's patruus magnus left him a valuable antique watch in his will.

The examples illustrate the definition of patruus magnus by showing how it refers to the brother of one's grandfather. In the first example, the speaker meets their grandmother's brother, who is their great-uncle. In the second example, the father's great-uncle left him an inheritance. Both examples demonstrate the relationship between a person and their patruus magnus.