Laugh nervously (6)
I believe the answer is:
giggle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">laugh nervously</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 giggle that I've seen before include "Laugh foolishly" , "Laugh nervously" , "Laugh in a silly manner" , "Titter" , "Foolish or nervous laugh" .)