Heaviness (6)
I believe the answer is:
weight
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">heaviness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(how much something weighs)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for weight that I've seen before include "Trouble" , "Attach importance to" , "Heavy load - preponderance" , "Heavy object" , "Importance, heaviness" .)