Field of operation’s area around the kidneys? Not entirely (5)
I believe the answer is:
arena
'field' is the definition.
(synonyms)
'operation's area around the kidneys? not entirely' is the wordplay.
I cannot really see how this works, but
'area' could be 'a' (maths abbreviation) and 'a' is found in the answer.
'around' could be 're' (regarding) and 're' is present in the answer.
The remaining letters 'na' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for arena that I've seen before include "centre of conflict" , "What the Colosseum was" , "combat zone" , "Area surrounded by seating, for sports, etc." , "Entertainments venue" .)