Entertainment logical in the X-ray dept.? (5)

I believe the answer is:

radio

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'entertainment' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I cannot understand how the remainder of the clue works.

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(Other definitions for radio that I've seen before include "Contact" , "Receiving set" , "Communicate with" , "listening device" , "Receiving apparatus" .)

I've seen this clue in the Evening Standard.

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