transponder

American  

[tran-spon-der] / trænˈspɒn dər /

Or transpondor

noun

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

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transponder British  

/ trænˈspɒndə /

noun

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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transponder Scientific  

/ trăn-spŏn′dər /

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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Etymology

Origin of transponder

First recorded in 1940–45; trans(mitter) + (res)ponder

Explanation

A transponder is a communication device that can either send or receive signals (or both). With a special transponder in your car, you can drive slowly through a tollbooth as your toll is collected electronically. The word transponder is what's known as a portmanteau, or a combination of two words into one — in this case, it comes from transmit and respond. Airplanes carry transponders that can communicate with the radar used by air traffic controllers on the ground, and race cars contain transponders that help time their laps accurately.

Example Sentences

See Examples For:

transponder

Having a transponder on board would have automatically alerted air traffic controllers that the aircraft and the truck were on a possible collision course, according to investigators.

From Barron's ● Apr. 23, 2026

That would be useful particularly if a ship has turned off its location transponder.

From The Wall Street Journal ● Apr. 9, 2026

The ship was off Muscat, Oman, early Friday, still broadcasting the message "owner France" on its transponder system in the field usually used to give the destination.

From Barron's ● Apr. 3, 2026

A Pakistani oil tanker transited the Strait of Hormuz with its automatic transponder system activated, monitor Marine Traffic said Monday, the first such voyage by a non-Iranian tanker since the start of the war.

From Barron's ● Mar. 16, 2026

"Tell him to hold, and verify on board transponder."

From Terminal Compromise: computer terrorism: when privacy and freedom are the victims: a novel by Schwartau, Winn