Unit of sound intensity (7)
I believe the answer is:
decibel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unit of sound intensity</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 decibel that I've seen before include "Unit for measuring intensity of sound" , "Measure of sound" , "I relate to volume" , "Level of noise" , "Noise unit" .)