Make fast turn in space (4)
I believe the answer is:
room
'space' is the definition.
(enough space or room to do something)
'make fast turn' is the wordplay.
'make fast' becomes 'moor' (mooring is a kind of making fast).
'turn' shows that the letters should be reversed in order.
'moor' backwards is 'ROOM'.
'in' acts as a link.
(Other definitions for room that I've seen before include "Enclosed part of building" , "Space; part of building" , "basic accommodation" , "Space (for elbows?)" , "Chamber; scope" .)