Rodgers and Hammerstein musical (8)
(Other definitions for oklahoma that I've seen before include "A holm oak found over in the States" , "Show" , "American state and great western musical" , "American state and famous musical" , "Look, a ham from the state" .)
'rodgers and hammerstein musical' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for the king and i that I've seen before include "Film/musical set in Siam" , "Rogers & Hammerstein musical" , "Bangkok-setting musical" , "Rodgers and Hammerstein musical" , "Show" .)