Writing about examination principles (6)
I believe the answer is:
morals
'principles' is the definition.
(thesaurus)
'writing about examination' is the wordplay.
'writing' becomes 'ms' (abbreviation for manuscript).
'about' is an insertion indicator.
'examination' becomes 'oral' (oral is a kind of examination).
'ms' enclosing 'oral' is 'MORALS'.
(Other definitions for morals that I've seen before include "Principles or rules of right and wrong" , "Generous; class" , "code?" , "High principles or ethics" , "Ethical motives" .)