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Medium greeting used for long-distance communication (5,4)

Ross

I believe the answer is:

radio wave

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'long-distance communication' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'medium greeting' is the wordplay.
'medium' becomes 'radio' (I've seen this in another clue).
'greeting' becomes 'wave' (I've seen this before).
'radio'+'wave'='RADIO WAVE'

'used for' acts as a link.

Can you help me to learn more?

(Other definitions for radio wave that I've seen before include "Long-distance message-carrier" , "Carrier of sound" , "Transmission signal" .)

I've seen this clue in The Daily Express.
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