Pest involved with current ill will (5)
I believe the answer is:
spite
'ill will' is the definition.
(I've seen this in another clue)
'pest involved with current' is the wordplay.
'involved with' is an anagram indicator (involved can mean confusing or complex).
'current' becomes 'I' (symbol for electric current).
'pest' mixed up with 'i' can make 'SPITE'.
(Other definitions for spite that I've seen before include "animosity" , "Desire to intentionally and maliciously hurt or offend" , "Malicious desire to hurt or humiliate" , "Hatred" , "Desire to hurt or annoy" .)