The capital of Saudi Arabia (6)
I believe the answer is:
riyadh
'the capital of saudi arabia' is the definition.
('Riyadh' can be a synonym of 'capital of saudi arabia')
This is the entire clue.
(Other definitions for riyadh that I've seen before include "Capital city of Saudi Arabia" , "Middle Eastern venue" , "Saudi Arabian city" , "Saudi Arabian capital" , "Arab capital" .)