Arena set for orchestral work (8)

I believe the answer is:

serenata

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'orchestral work' is the definition.
The definition suggests a singular noun which matches the answer.

'arena set' is the wordplay.
'arena set' can be anagrammed to 'SERENATA'.
However, I am not clear how the anagram is indicated.

'for' is the link.

Can you help me to learn more?

(Other definitions for serenata that I've seen before include "Musical composition" , "piece of music" , "Country work" , "Notes" , "Pastoral cantata" .)

I've seen this clue in The Irish Independent.

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