Elementary, simple (5)
I believe the answer is:
basic
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">elementary</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">simple</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for basic that I've seen before include "Fundamental; alkaline" , "At the lowest level" , "Fundamental or rudimentary" , "Elemental" , "Key" .)