Tune; topic (5)
I believe the answer is:
theme
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">tune</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that theme is a type of tune)</span><br/ ><br/ >'<span class="explanation-format__original">topic</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that topic can be written as theme)</span><br/ ><br/ ></span>
(Other definitions for theme that I've seen before include "Motif, topic" , "Main idea or topic" , "tune used in Enigma Variations?" , "Topic for discussion" , "argument" .)