Balancer n. : One who balances, or uses a balance.

Balancer n. : In Diptera, the rudimentary posterior wing.

Example:
How to uninstall a harmonic Balancer on a 1980 Bronco with a 351M motor?

Taxonomy
Balancer, Southwest, models, Aluminum, Model Aircraft, AMA, weights, perfect balance, All New, S&H, fuselages, Dealers, Product Specifications, MODEL PRODUCTS, kit, APPOINTMENT, THE UNITED KINGDOM, EUROPEAN CUSTOMERS.

Defination from the web:
Balancer is shown with a Composite ARF 3.1-meter Extra which weighs approximately 42 lbs., and has a wingspan of 124" ... Southwest Systems All New All Aluminum EZ Balancer II not only handles everything the original did, but it is much more versatile and will handle ...