• synonyms


or tran·spon·dor

  1. a radio, radar, or sonar transceiver that automatically transmits a signal upon reception of a designated incoming signal.
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Origin of transponder

First recorded in 1940–45; trans(mitter) + (res)ponder
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for transponder



  1. a type of radio or radar transmitter-receiver that transmits signals automatically when it receives predetermined signals
  2. the receiver and transmitter in a communications or broadcast satellite, relaying received signals back to earth
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Word Origin

C20: from transmitter + responder
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for transponder


1945, from trans(mit) + (res)pond + agent noun suffix -er (1).

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Online Etymology Dictionary, © 2010 Douglas Harper

transponder in Science


  1. A radio or radar transmitter and receiver that responds to an incoming signal either by broadcasting its own predetermined signal (as in aircraft identification systems) or by relaying the incoming signal at a different frequency (as in satellite communications).
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.