Mental grasp (6)
I believe the answer is:
uptake
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mental grasp</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for uptake that I've seen before include "Level of acceptance" , "Put off until later" , "understanding" , "Acceptance of offer" , "Mental grasp" .)