Musical setting for Mamma Mia!, from the soundtrack? (6)

I believe the answer is:

grease

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'musical' is the definition.
(Grease is a film musical)

I don't understand how the remainder of the clue works.

(Other definitions for grease that I've seen before include "Lubricate - musical" , "Rock musical" , "Thick lubricant or frying oil" , "Musical - lubricant" , "Fatty lubricant" .)

I've seen this clue in The Telegraph.

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