Verb (used with object) : to reciprocate favors.    From Dictionary.com. 

Reputation is important, and biologists can acknowledge a Darwinian survival value in not just being a good reciprocator but fostering a reputation as a good reciprocator too.    From Wordnik.com.  [The God Delusion]

Third, the lay shaft driving the governor oil pump and reciprocator is located underneath the main turbine shaft, so that the rotor may be readily removed without in the least disturbing the governor adjustment.    From Wordnik.com.  [Steam Turbines A Book of Instruction for the Adjustment and Operation of the Principal Types of this Class of Prime Movers] Reference