Show displeasure (4)
I believe the answer is:
hiss
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">show displeasure</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for hiss that I've seen before include "Urgently whisper" , "Catcall" , "Sound of serpent" , "less welcome sign?" , "Boo" .)