A countervailing force, power, or opinion is one which is of equal strength to another one but is its opposite or opposes it.
例句
Their strategy is expansionist and imperialist, and it is greatest in effect, of course, when there is no countervailing power...他们的策略是扩张性的、带有帝国主义特色，当没有抗衡力量的时候自然也就被发挥到了极致。There were two central and countervailing forces in the life of Nikola Tesla.在尼古拉·特斯拉的生活中存在着两股非常重要而且相互抗衡的力量。