Dim piece could produce widespread complaint (8)
I believe the answer is:
epidemic
'widespread complaint' is the definition.
'epidemic' can be an answer for 'complaint' (I've seen this before). I am not sure about the 'widespread' bit.
'dim piece could produce' is the wordplay.
'could produce' indicates anagramming the letters (I've seen this in other clues).
'dim'+'piece'='dimpiece'
'dimpiece' anagrammed gives 'EPIDEMIC'.
Can you help me to learn more?
(Other definitions for epidemic that I've seen before include "Widespread outbreak of an infectious disease" , "Unfortunately widespread" , "Widespread occurrence of a disease" , "medical emergency" , "Fast food item" .)