WordNet sense 1 (equality of distribution):

balance, equilibrium, equipoise

WordNet sense 2 (a compensating equivalent):

offset

WordNet sense 3 (a weight that balances another weight):

counterpoise, counterweight, equalizer, equaliser

WordNet sense 4 (adjust for):

compensate, correct, make up, even up, even off, even out

WordNet sense 5 (oppose with equal weight or force):

oppose

WordNet sense 6 (oppose and mitigate the effects of by contrary actions):

counteract, countervail, neutralize