Region bordering the Rhine (4)
I believe the answer is:
ruhr
'region bordering the rhine' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ruhr that I've seen before include "industrial valley" , "Ger. industrial region" , "Traditional region of German heavy industry" , "German river flowing into the Rhine" , "German industrial zone, river" .)