Lack of enthusiasm (6)
I believe the answer is:
apathy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lack of enthusiasm</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 apathy that I've seen before include "Complete lack of interest, indifference" , "Indifferent quality" , "Indifference - listlessness" , "lack of involvement" , "Indifference, emotionlessness" .)