Finger sound (4)
I believe the answer is:
snap
'finger sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for snap that I've seen before include "Break sharply like dried twig" , "Photograph - card game" , "Take a photo" , "Go to pieces < , it's said, quickly" , "Break under strain" .)