Accountant plugs something essential to make capital (6)
I believe the answer is:
muscat
'capital' is the definition.
(capital of Oman)
'accountant plugs something essential' is the wordplay.
I cannot really understand how this works, but
'accountant' could be 'ca' (abbreviation for chartered accountant) and 'ca' is found in the answer.
'essential' could be 'must' (similar in meaning) and 'must' is present in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'to make' acts as a link.
Can you help me to learn more?
(Other definitions for muscat that I've seen before include "Type of grape and the capital of Oman" , "Arabic port" , "Source of alcoholic drink" , "wine producer" , "Sweet white wine - Omani port" .)