Definition of transponder noun from the Oxford Advanced Learner's Dictionary

 

transponder

 noun
noun
BrE BrE//trænsˈpɒndə(r)//
 
; NAmE NAmE//trænsˈpɑːndər//
 
(specialist)
 
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a piece of equipment that receives radio signals and automatically sends out another signal in reply Word Origin 1940s: blend of transmit and respond, + -er.
See the Oxford Advanced American Dictionary entry: transponder