Space around to tie up (4)
I believe the answer is:
moor
'tie up' is the definition.
(as in mooring a boat)
'space around' is the wordplay.
'space' becomes 'room' (enough space or room to do something).
'around' is a reversal indicator.
'room' written backwards gives 'MOOR'.
'to' is the link.
(Other definitions for moor that I've seen before include "eg Ilkley, Othello" , "Open expanse covered with heather and bracken" , "Wild land; tie up" , "Use ropes to secure" , "Tract of uncultivated upland" .)