Concept, belief (6)
I believe the answer is:
notion
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">concept</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(notion is a kind of concept)</span><br/ ><br/ >'<span class="explanation-format__original">belief</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for notion that I've seen before include "Vague understanding" , "Vague impression" , "An idea or casual thought" , "Whimsical idea or small sewing article" , "Vague idea or opinion" .)