What is Ex Gravy Querela?

Legal Definition
(From or on the grievous complaint.) In old English practice. The name of a writ (se called from its initial words) which lay for a person to whom any lands or tenements in fee were devised by will, (within any city, town or borough wherein lands were devisable by custom,) and the heir of the devisor entered and detained them from him. Fitzh. Nat. Brev. 198, L, et seq.; 3 Reeve, Eng. Law, 49. Abolished by St. 3 & 4 Wm. IV. c. 27, ยง 36.
-- Black's Law Dictionary