Source : Webster's Revised Unabridged Dictionary (1913)

Balancer \Bal"an*cer\, n.
   1. One who balances, or uses a balance.

   2. (Zo["o]l.) In Diptera, the rudimentary posterior wing.

Source : WordNet®

balancer
     n 1: an acrobat who balances himself in difficult positions
     2: either of the club-like rudimentary hind wings of dipterous
        insects; used for maintaining equilibrium during flight
        [syn: {halter}, {haltere}]