A killjoy like Harpagon getting left out (6)
I believe the answer is:
misery
'a killjoy' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for misery that I've seen before include "Great distress or discomfort" , "Wretched conditions" , "Distress, wretchedness" , "Torment" , "Wretched state" .)