Complaint about displacing holy man from Northern Ireland (5)
I believe the answer is:
ulcer
'complaint' is the definition.
(a medical complaint)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ulcer that I've seen before include "Cruel form of stomach trouble?" , "cause of suffering" , "Stomach or mouth sore" , "Cruel kind of bodily sore" , "Cruel sort of body sore" .)