Musical state (8)
I believe the answer is:
This clue is a double definition.
'musical' is the first definition.
(I've seen this before)
'state' is the second definition.
(I know that Oklahoma is a state)
(Other definitions for oklahoma that I've seen before include "S. central US state" , "US State and musical drama" , "US state, joined in 1907" , "A holm oak for a musical" , "Look, a ham from the state" .)