1) Acrobat 2) Cattle breed 3) Fly appendage 4) Gymnast, often 1) Haltere 2) Poiser 
Balancer are a hybrid breed of beef cattle, a combination of Gelbvieh and Angus. These cattle are bred for their hybrid vigour, resulting in a higher growth rate and better quality meat. ...
• (n.) In Diptera, the rudimentary posterior wing. • (n.) One who balances, or uses a balance.
(from the article `amphibian`) ...hatching. In contrast, the limbs of anurans do not appear until after hatching. Soon after the appearance of forelimbs, most pond-dwelling ...
Bal'an·cer noun 1. One who balances, or uses a balance. 2. (Zoology) In Diptera, the rudimentary posterior wing. 
[n] - an acrobat who balances himself in difficult positions
noun an acrobat who balances himself in difficult positions