Source : Webster's Revised Unabridged Dictionary (1913)

Tresayle \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.