Acuteness (8)
I believe the answer is:
severity
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">acuteness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for severity that I've seen before include "Sternness" , "Harshness, asperity" , "Intensity; harshness" .)