The sound of a donkey (6)
I believe the answer is:
heehaw
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">the sound of a donkey</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for heehaw that I've seen before include "Cry of donkey" , "Horse-laugh" , "Imitation of a donkey's sound" , "Sound from the stable?" , "Ass's bray" .)