OneNote audio input extension (7)

I believe the answer is:

antenna

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'extension' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for antenna that I've seen before include "Insect's feeler" , "could send out a message" , "connected to 41?" , "Transmitting aerial" , "What detects signals" .)

I've seen this clue in The Guardian.

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