Kind of hat for singing in? (5)

I believe the answer is:

opera

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'kind of hat' is the definition.
(I've seen this in another clue)

I can't explain the rest of the clue.

(Other definitions for opera that I've seen before include "Verdi work?" , ""The Magic Flute", for example" , "Tosca, for example" , ""Rigoletto", for example" , "One with soap perhaps" .)

I've seen this clue in the Evening Standard.

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