Underlying theme (7)
I believe the answer is:
subtext
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">underlying theme</span>' is the definition.<br/ ><span class="explanation-format__explanation">(a secondary theme or message)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for subtext that I've seen before include "Something implied" , "Unwritten meaning" , "Level of deeper meaning" , "Underlying theme" , "Implicit meaning" .)