coun•ter•vailPronunciation: (koun"tur-vāl'), [key]
to act or avail against with equal power, force, or effect; counteract.
to furnish an equivalent of or a compensation for; offset.
to be of equal force in opposition; avail.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.