Nottingham’s river (5)
I believe the answer is:
trent
'nottingham's river' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for trent that I've seen before include "River at Stoke and Burton" , "Midlands banker" , "Main river of the Midlands" , "Chief river of the Midlands" , "Notts. river" .)