Cambridgeshire 'isle' (3)
I believe the answer is:
ely
'cambridgeshire isle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ely that I've seen before include "Cambs cathedral" , "Cathedral city in Cambridgeshire" , "'Isle' in Cambridgeshire" , "Fenland cathedral town" , "Small city in Cambridgeshire" .)