In brief, fine state of musical theatre (8)

I believe the answer is:

oklahoma

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

'in brief fine state of musical' is the definition.
'oklahoma' can be an answer for 'musical' (I've seen this before). I'm not sure about the 'in brief fine state of' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for oklahoma that I've seen before include "US state - Rodgers and Hammerstein musical" , "state of America" , "OK" , "American state and famous musical" , "US State and musical drama" .)

I've seen this clue in The Guardian.

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