Tomato impact sound (5)
I believe the answer is:
splat
'tomato impact sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for splat that I've seen before include "Sound of a soft, wet object striking a surface" , "Wet slapping sound" , "Sound of a soft wet landing" , "Noise of soft wet impact; part of a chair back" , "amusing noise" .)