Essential point (4)
I believe the answer is:
crux
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">essential point</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 crux that I've seen before include "Essential point in the matter or problem" , "puzzle" , "Core" , "Decisive, baffling, point" , "Essence or gist" .)