to act or avail against with equal power, force, or effect; counteract.
2.
to furnish an equivalent of or a compensation for; offset.
3.
Archaic.to equal.
verb (used without object)
4.
to be of equal force in opposition; avail.
Origin: 1350–1400;Middle Englishcontrevailen < Anglo-Frenchcountrevail-, tonic stem (subjunctive) of countrevaloir to equal, be comparable to < Latin phrase contrā valēre to be of worth against (someone or something). See counter-, -valent
late 14c., "to be worth as much as," also "to prevail against," from Anglo-Fr. countrevaloir, O.Fr. contrevaloir, from L. phrase contra valere "to be worth against" (see contra and valiant). Related: Countervailing (1610s).