Slight wave (6)
I believe the answer is:
ripple
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">slight wave</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ripple that I've seen before include "Slight disturbance on water's surface" , "A small wave, or a gentle sound as of laughter" , "undulation" , "Light ruffle on the surface" , "Edgar Allan ---, US author" .)