Sharp-witted (6)
I believe the answer is:
astute
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sharp-witted</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for astute that I've seen before include "Subtle" , "Shrewd, canny" , "Having hardheaded intelligence" , "Shrewd and clever" , "smart (with some self-interest?)" .)