Professional army officer keeping to correct procedure (8)
I believe the answer is:
protocol
'correct procedure' is the definition.
(I've seen this before)
'professional army officer keeping to' is the wordplay.
'professional' becomes 'pro' ('pro' can be a synonym of 'professional').
'army officer' becomes 'col' (I've seen this in other clues).
'keeping' means one lot of letters goes inside another.
'pro'+'col'='procol'
'procol' placed around 'to' is 'PROTOCOL'.
(Other definitions for protocol that I've seen before include "Procedure or system of rules" , "Draft treaty" , "Poor clot involved in kind of status etiquette" , "Approved procedure" , "customs" .)