Ponte Vecchio river (4)
I believe the answer is:
arno
'ponte vecchio river' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arno that I've seen before include "River in central Italy" , "River flowing through Florence and Pisa" , "Italian river" , "River of 11 across" , "River in Tuscany" .)