The Collaborative International Dictionary of English v.0.48:

counter-balanced \counter-balanced\ counterbalanced
\counterbalanced\adj.
   brought into equipoise by means of a weight or force that
   offsets another.

   Syn: counterpoised.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Counterbalance \Coun`ter*bal"ance\ (-b?l"ans), v. t. [imp. & p.
   p. Counterbalanced (-anst); p. pr. & vb. n.
   Counterbalancing.]
   To oppose with an equal weight or power; to counteract the
   power or effect of; to countervail; to equiponderate; to
   balance.
   [1913 Webster]

         The remaining air was not able to counterbalance the
         mercurial cylinder.                      --Boyle.
   [1913 Webster]

         The study of mind is necessary to counterbalance and
         correct the influence of the study of nature. --Sir W.
                                                  Hamilton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

counterbalanced
    adj 1: brought into equipoise by means of a weight or force that
           offsets another [syn: counterbalanced, counterpoised]