Small wave (6)
I believe the answer is:
ripple
'small wave' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ripple that I've seen before include "A small wave, or a gentle sound as of laughter" , "Slight surface wave" , "Slight disturbance on water's surface" , "Type of ice cream with coloured syrup" , "Small wave or surface disturbance" .)