Long poem cut by half causes widespread ill-feeling (8)
I believe the answer is:
epidemic
'widespread ill-feeling' is the definition.
I can't judge whether this defines the answer.
'long poem cut by half' is the wordplay.
'long poem' becomes 'epic' (I've seen this in another clue).
'cut by' indicates putting letters inside (some letters cut into others).
'half' becomes 'demi' (prefix as in 'demigod').
'epic' enclosing 'demi' is 'EPIDEMIC'.
'causes' acts as a link.
Can you help me to learn more?
(Other definitions for epidemic that I've seen before include "Widespread infection" , "Unfortunately widespread" , "Widespread outbreak of an infectious disease" , "Fast food item" , "Prevailing" .)