Major industrial region of north-west Germany (4)
I believe the answer is:
ruhr
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">major industrial region of north-west germany</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ruhr that I've seen before include "German industrial zone, river" , "German industrial region" , "Ger. industrial region" , "industrial valley" , "Traditional region of German heavy industry" .)