Lower world (5)
I believe the answer is:
hades
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lower world</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for hades that I've seen before include "Hell of Greek myth" , "Inferno" , "A place of some darkness" , "It's classical hell in the shade" , "Greek underworld with spirits of the dead" .)