Scat singer Fitzgerald (4)
I believe the answer is:
ella
'scat singer fitzgerald' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ella that I've seen before include "Great late jazz singer . . . . Fitzgerald" , "Girl" , "Diminutive of Eleanor" , "Ms Fitzgerald" , "---- Fitzgerald, 'Queen of Jazz'" .)