What is Grand Assize?

Legal Definition
A peculiar species of trial by jury, introduced in the time of Henry II., giving the tenant or defendant in a writ of right the alternative of a trial by battel, or by his peers. Abolished by 3 & 4 Wm. IV. c. 42, § 13. See 3 Bl. Comm. 341.
-- Black's Law Dictionary
Legal Definition
A substitute for trial by battel before a jury of sixteen men. See 3 Bl. Comm. 341.
-- Ballentine's Law Dictionary