The Collaborative International Dictionary of English v.0.48:

Counterpoise \Coun"ter*poise`\ (koun"t?r-poiz`; 277), v. t.
   [imp. & p. p. Counterpoised (-poizd`); p. pr. & vb. n.
   Counterpoising.] [OE. countrepesen, counterpeisen, F.
   contrepeser. See Counter, adv., and Poise, v. t. ]
   1. To act against with equal weight; to equal in weight; to
      balance the weight of; to counterbalance.
      [1913 Webster]

            Weights, counterpoising one another.  --Sir K.
                                                  Digby.
      [1913 Webster]

   2. To act against with equal power; to balance.
      [1913 Webster]

            So many freeholders of English will be able to beard
            and counterpoise the rest.            --Spenser.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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