\Tres"ayle`\ (tr[e^]s"[=a]l`), n. [F. trisa["i]eul,
from L. tris, tres, three + F. a["i]eul grandfather. Cf.
{Besaiel}, and see {Ayle}.]
A grandfather's grandfather. [Obs.]
{Writ of tresayle} (O. Eng. Law), a writ which lay for a man
   claiming as heir to his grandfather's grandfather, to
   recover lands of which he had been deprived by an
   abatement happening on the ancestor's death. --Mozley & W.