Observed to lead signora to riotous musical work (8)

I believe the answer is:

oratorio

I'm a little stuck... Click here to teach me more about this clue!

'musical work' is the definition.
(I've seen this before)

'observed to lead signora to riotous' is the wordplay.
'ORATORIO' is hidden within the letters.
However, I am not sure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for oratorio that I've seen before include "Work for voices, chorus and orchestra with biblical theme" , "I, too, roar at musical composition with Biblical theme" , "Work performed by choir" , "Religious musical drama, unstaged" , "Sacred, dramatic music" .)

I've seen this clue in the Sydney Morning Herald.

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