countervail
Concise Oxford English Dictionary © 2008 Oxford University Press:
countervail /ˌkaʊntəˈveɪl/
▶verb (usu. as adj. countervailing) offset the effect of (something) by countering it with something of equal force.
– origin ME: from Anglo-Norman Fr. contrevaloir, from L. contra valere ‘be of worth against’.
'countervail' also found in these Oxford entries:

