Adviser thought to have advanced to highest level (4)
I believe the answer is:
aide
'adviser' is the definition.
'thought to have advanced to highest level' is the wordplay.
I cannot quite understand how this works, but
'advanced' could be 'a' and 'a' is present in the answer.
The remaining letters 'ide' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for aide that I've seen before include "Right-hand man/woman" , "Officer in attendance" , "Political assistant" , "Assistant to a more senior person" , "Leader's assistant" .)