Singer ____ Campbell (4)
I believe the answer is:
glen
'singer campbell' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for glen that I've seen before include "Narrow valley with a stream" , "Narrow, deep mountain valley" , "Valley, dale" , "Narrow secluded valley in mountains" , "Narrow Scots valley" .)