Lower, under (6)
I believe the answer is:
nether
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">lower</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(as in nether regions)</span><br/ ><br/ >'<span class="explanation-format__original">under</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for nether that I've seen before include "Subordinate" , "inferior" , "These garments are for the bottom half" , "These regions are hell, the underworld" , "Lower, like regions or garments" .)