Level, even (4)
I believe the answer is:
flat
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">level</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">even</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ ></span>
(Other definitions for flat that I've seen before include "Level - uninteresting - accommodation" , "In music, below the correct pitch" , "Small residence - lacking sparkle" , "Absolutely" , "No longer charged" .)