Bottom, foundation (4)
I believe the answer is:
base
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">bottom</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(base is a kind of bottom)</span><br/ ><br/ >'<span class="explanation-format__original">foundation</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for base that I've seen before include "Mean; HQ" , "Pedestal" , "Plinth" , "Lowest part; ignoble" , "Ignoble; starting point" .)