Light musical drama (8)
I believe the answer is:
operetta
'light musical drama' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for operetta that I've seen before include "Patience perhaps" , "Eg, Orpheus in the Underworld" , "Musical entertainment" , "Light opera" , "The Mikado, e.g." .)