Turkish officer secures right site for mausoleum (4)
I believe the answer is:
agra
'site for mausoleum' is the definition.
The definition suggests a singular noun which matches the answer.
'turkish officer secures right' is the wordplay.
'turkish officer' becomes 'aga' (military commander eg in the Ottoman Empire).
'secures' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'aga' enclosing 'r' is 'AGRA'.
Can you help me to learn more?
(Other definitions for agra that I've seen before include "Indian masterpiece" , "Foreign city" , "includes Taj Mahal" , "North Indian city, former capital of the Mogul empire" , "Taj Mahal city" .)