What is Est Ascavoir?

Legal Definition
It Is to be understood or known; "it ls to-wlt" Litt. §§ 9, 45, 46, 57, 59. A very common expression in Littleton, especially at the commencement of a section; and, according to Lord Coke, "it ever teacheth us some rule of law or general or sure leading point" Co. Litt. 16.
-- Black's Law Dictionary
Legal Definition
It is understood; viz.
-- Ballentine's Law Dictionary