List of rules in old literature carried by professional officer (8)
I believe the answer is:
protocol
'list of rules' is the definition.
'protocol' can be an answer for 'rules' (I have seen 'Procedural rules ' mean 'protocol' so perhaps 'rules' could also mean 'protocol'). I am not certain of the 'list of' bit.
'old literature carried by professional officer' is the wordplay.
'old literature' becomes 'ot' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'carried by' means one lot of letters goes inside another.
'professional' becomes 'pro' ('pro' can be a synonym of 'professional').
'officer' becomes 'col' (I've seen this before).
'ot' going into 'pro' is 'proto'.
'proto'+'col'='PROTOCOL'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for protocol that I've seen before include "Procedure or system of rules" , "Good form" , "Correct procedure" , "Formalities" , "customs" .)