At heart, fundamentally (2,7)
I believe the answer is:
in essence
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">at heart</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">fundamentally</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for in essence that I've seen before include "Fundamentally" , "Basically" , "Substantially" , "at bottom" .)