Agrees about musical (6)
I believe the answer is:
grease
'musical' is the definition.
(Grease is a film musical)
'agrees about' is the wordplay.
'about' indicates anagramming the letters.
'agrees' is an anagram of 'GREASE'.
(Other definitions for grease that I've seen before include "Musical animal fat?" , "Musical - lubricant" , "Possible cause of slip-up" , "Fully aware, astonished" , "Musical starring John Travolta and Olivia Newton-John" .)