Jazz singing style (4)
I believe the answer is:
scat
'jazz singing style' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scat that I've seen before include "it's dropped by 21 [SNAKES]" , "Bolt" , "Style of jazz singing" , "Wordless singing style" , ""Beat It"" .)