Fell in dock (4)
I believe the answer is:
moor
I believe this clue is a double definition.
'fell' is the first definition.
(fell can mean a moor or hill)
'dock' is the second definition.
(I know that dock is a is a more specific form of the action of moor)
'in' acts as a link.
(Other definitions for moor that I've seen before include "Open expanse covered with heather and bracken" , "Desolate area" , "Upland tract - eg Othello" , "African - wasteland" , "See 5 Down" .)