|Noah Webster's Dictionary|
1. (v. t.) To offset; to act against with equal force, power, or effect; to thwart or overcome by such action; to furnish an equivalent to or for; to counterbalance; to compensate.
2. (n.) Power or value sufficient to obviate any effect; equal weight, strength, or value; equivalent; compensation; requital.
Int. Standard Bible Encyclopedia
koun-ter-val' (shawah, "equalize"): To thwart or overcome by acting against with equal force; thus, "The enemy could not countervail the king's damage" or loss (Esther 7:4 the American Standard Revised Version reads "The adversary could not have compensated for the king's damage"). "Nothing doth countervail (the Revised Version (British and American) "can be taken in exchange for") a faithful friend" (Ecclesiasticus 6:15).
Countervail (1 Occurrence)
Esther 7:4 For we are sold, I and my people, to be destroyed, to be slain, and to perish. But if we had been sold for bondmen and bondwomen, I had held my tongue, although the enemy could not countervail the king's damage. (KJV WBS)