Shrewd, perceptive (6)
I believe the answer is:
astute
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">shrewd</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that shrewd can be written as astute)</span><br/ ><br/ >'<span class="explanation-format__original">perceptive</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for astute that I've seen before include "Able to assess (people or situations) accurately" , "Discerning" , "intelligent" , "Shrewd, quick to spot advantage" , "Canny and sagacious" .)