Lack of energy and enthusiasm (8)
I believe the answer is:
lethargy
'lack of energy and enthusiasm' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lethargy that I've seen before include "'Lassitude, langour (8)'" , "Lassitude, languor" , "Sloth" , "Extreme lack of energy, listlessness" , "Weariness" .)