Source : Webster's Revised Unabridged Dictionary (1913)

Overbalance \O`ver*bal"ance\, v. t.
   1. To exceed equality with; to outweigh. --Locke.

   2. To cause to lose balance or equilibrium.

Overbalance \O"ver*bal`ance\, n.
   Excess of weight or value; something more than an equivalent;
   as, an overbalance of exports. --J. Edwards.

Source : WordNet®

overbalance
     v 1: weigh more heavily [syn: {preponderate}, {outweigh}, {outbalance}]
     2: out out of; "It is not desirable to overbalance the budget"