What is Bisaile?

Legal Definition
Domestic relations. A corruption of the French word besaieul, the father of the grandfather or grandmother. In Latin he is called proavus. Inst. 3, 6, 3 Dig. 38, 10, 1, 5. Vide Aile.
-- Bouviers Law Dictionary
Legal Definition
The father of one's grandfather or grandmother.
-- Black's Law Dictionary