Dock, reversing into berth (4)
I believe the answer is:
room
'berth' is the definition.
(thesaurus)
'dock reversing' is the wordplay.
'dock' becomes 'moor' (I've seen this in other clues).
'reversing' says the letters should be written in reverse.
'moor' written backwards gives 'ROOM'.
'into' is the link.
(Other definitions for room that I've seen before include "kitchen?" , "Place" , "Enclosed space in a building" , "Enclosed part of building" , "Box ---, storage area" .)