Lowest part; ignoble (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">lowest part</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">ignoble</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ ></span>
(Other definitions for base that I've seen before include "Ignoble, military site" , "Plinth" , "Low kind of foundation" , "home?" , "Infamous" .)