counterpoise

Short definition from Wiktionary

Noun

1. 1
   A weight sufficient to balance another, for example in the opposite end of scales; an equal weight.
2. 2
   An effect of equal power or force acting in opposition; a force sufficient to balance another force or influence
3. 3
   The relation of two weights or forces which balance each other; equilibrium

Verb

1. 1
   To act against with equal weight; to equal in weight; to balance the weight of; to counterbalance.
2. 2
   To act against with equal power; to balance.