Shrewd; sharp-witted (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">sharp-witted</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 make accurate assessments" , "Clever and perceptive" , "Sharp-witted" , "Shrewd, canny" , "Canny and sagacious" .)