Origin: 1350–1400; Middle English contrevailen < Anglo-French countrevail-, 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).