Reflection of sound (4)
I believe the answer is:
echo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">reflection of sound</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 echo that I've seen before include "Sound following" , "She loved Narcissus - it's recalled" , "Reflection of sound - Greek nymph" , "Sound heard before" , "Before foxtrot" .)