Furthest down (6)
I believe the answer is:
lowest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">furthest down</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lowest that I've seen before include "most depressed" , "Least high" , "Nethermost" , "Given maximum reduction" , "Owlets at the bottom level" .)