To nick spy chief follows decorum (14)
I believe the answer is:
misappropriate
'to nick' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for misappropriate that I've seen before include "embezzle" , "Nick" , "Unfairly take for one's own use" , "Lift" , "Steal, take unfairly" .)