The Collaborative International Dictionary
Tresayle
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.
Wiktionary
tresayle
n. (context obsolete English) A grandfather's grandfather.