Senior diplomat's fuss over retreat set up by American singer (13)
I believe the answer is:
ambassadorial
'senior diplomat's' is the definition.
(I know this)
'fuss over retreat set up by american singer' is the wordplay.
I cannot really understand how this works, but
'fuss' could be 'ado' (synonyms) and 'ado' is found within the answer.
'american' could be 'am' (abbreviation in some contexts) and 'am' is located in the answer.
'singer' could be 'bass' (bass is a kind of singer) and 'bass' is located in the answer.
The remaining letters 'rial' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ambassadorial that I've seen before include "Relating to the highest diplomatic duties" , "suitable for diplomats" , "Relating to a country's representative abroad" .)