Study of morality (6)
I believe the answer is:
ethics
'study of morality' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ethics that I've seen before include "rules of conduct" , "Codes of standards in business" , "Moral principles in middle" , "Codes of conduct in business affairs" , "Study of moral values and rules" .)