Trenchant; acute (8)
I believe the answer is:
incisive
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">trenchant</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">acute</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that acute can be written as incisive)</span><br/ ><br/ ></span>
(Other definitions for incisive that I've seen before include "Analytical, concise" , "Clear and probing, trenchant" , "Clear and cutting" , "Intelligently analytical and clear-thinking" , "Piercing" .)