Lowest or deepest point (5)
I believe the answer is:
nadir
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">lowest</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">deepest point</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for nadir that I've seen before include "lowest of the low" , "All-time low" , "Point of greatest despair" , "Drain to lowest level" , "Point opposite the zenith" .)