Letters to revise with approval (6)
I believe the answer is:
credit
'approval' is the definition.
(I know that credit is a type of approval)
'letters to revise' is the wordplay.
'letters' becomes 'cr' (I can't explain this - if you can you should give a lot more credence to this answer).
'to revise' becomes 'edit' (I've seen this before).
'cr'+'edit'='CREDIT'
'with' is the link.
Can you help me to learn more?
(Other definitions for credit that I've seen before include "Approval" , "support for one with money problems" , "Belief; tick" , "Acknowledgement in a book" , "Believe; good reputation" .)