Tie up revolutionary to get space (4)
I believe the answer is:
room
'space' is the definition.
(room is a kind of space)
'tie up revolutionary' is the wordplay.
'tie up' becomes 'moor' (I've seen this before).
'revolutionary' says the letters should be written backwards.
'moor' in reverse letter order is 'ROOM'.
'to get' is the link.
(Other definitions for room that I've seen before include "Place" , "Scope; living space" , "Enclosed space in a building" , "See 17" , "Space, area" .)