Writers using a concealed crib (7)
I believe the answer is:
scribes
'writers' is the definition.
(scribe is a kind of writer)
'using a concealed crib' is the wordplay.
'using' becomes 'ses' (I can't explain this - if you can you should believe this answer much more).
'a concealed' means one lot of letters goes inside another.
'ses' enclosing 'crib' is 'SCRIBES'.
Can you help me to learn more?
(Other definitions for scribes that I've seen before include "Copyists" , "journos" , "Ancient writers (7)" , "People who once made hand-written copies" .)