High-five sound (4)
I believe the answer is:
slap
'high-five sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slap that I've seen before include "Hit with an open hand" , "A blow among pals" , "Blow (in face, on back, wrist)" , "Strike action" , "Sharp smack" .)