In an unfriendly way, it was much sent up in Germany (4)

I believe the answer is:

flak

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'in an' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I don't see?

I cannot understand how the remainder of the clue works.

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(Other definitions for flak that I've seen before include "Anti-aircraft shells or adverse criticism" , "Shooting" , "Unfriendly criticism" , "heated disagreement" , "Brickbats" .)

I've seen this clue in the Evening Standard.

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