Loudness (6)
I believe the answer is:
volume
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">loudness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for volume that I've seen before include "A book or sound dimension" , "Cubic capacity" , "A book, especially one of a set" , "work" , "Book - measure of loudness" .)