Feeling of listlessness (5)
I believe the answer is:
ennui
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">feeling of listlessness</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 ennui that I've seen before include "Listless feeling" , "having nothing to do" , "Feeling when tired of life?" , "Mental weariness" , "Weariness with life" .)