To act against with equal force, power, or effect; to thwart or overcome by such action; to furnish an equivalent to or for; to counterbalance; to compensate.

Power or value sufficient to obviate any effect; equal weight, strength, or value; equivalent; compensation; requital.

compensate for or counterbalance; "offset deposits and withdrawals"

oppose and mitigate the effects of by contrary actions; "This will counteract the foolish actions of my colleagues"