Formal document incorporating a copyright stamp (9)
I believe the answer is:
character
'stamp' is the definition.
(thesaurus)
'formal document incorporating a copyright' is the wordplay.
'formal document' becomes 'charter' (charter is a kind of document. I am not sure about the 'formal' bit.).
'incorporating' is an insertion indicator.
'copyright' becomes 'C' (as in the copyright symbol, a C in a circle).
'a'+'c'='ac'
'charter' going around 'ac' is 'CHARACTER'.
Can you help me to learn more?
(Other definitions for character that I've seen before include "Amusing individual" , "Letter or number" , "Stamp < letter" , "Distinctive nature" , "Make-up" .)