Top brass stops over as secrets are dispatched (7)
I believe the answer is:
'secrets are dispatched' is the definition.
I can't judge whether this definition defines the answer.
'top brass stops over' is the wordplay.
'top brass' becomes 'co' (I can't explain this - if you can you should believe this answer much more).
'stops' means one lot of letters goes inside another.
'over' becomes 'ended' (synonyms).
'co' inserted within 'ended' is 'ENCODED'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for encoded that I've seen before include "as secrets are dispatched?" , "In cryptic version" , "formed in a difficult-to-understand way" , "Deed con (anag.)" .)