What is Avunculus?

Legal Definition
In the civil law. A mother's brother. 2 Bl. Comm. 230. Avunculus magnus, a great-uncle. Avunculus major, a great-grandmother's brother. Avunculus maximum, a great-great-grandmother's brother. See Dig. 38, 10, 10; Inst. 3, 6, 2.
-- Black's Law Dictionary