Intellectual capacity (5)
I believe the answer is:
brain
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">intellectual capacity</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 brain that I've seen before include "Encephalon" , "Intelligent person" , "Thinking thing" , "Clever person" , "Seat of the intellect" .)