Principles require writing off half of core debt (4)
I believe the answer is:
code
'principles' is the definition.
(a moral code)
'require writing off half of core debt' is the wordplay.
I cannot quite understand how this works, but
'writing' could be 'ode' (ode is a kind of writing) and 'ode' is found within the answer.
A single letter 'c' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for code that I've seen before include "Cypher" , "(Computer) programming instructions" , "Post -; dialling -" , "Program instruction" , "difficult to read" .)