Pang of conscience (5)
I believe the answer is:
qualm
'pang of conscience' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for qualm that I've seen before include "Scruple" , "Uneasy feeling" , "Anxiety" , "Misgiving, pang of conscience" , "Uneasiness of conscience" .)