Coast not bound to turn (9)
I believe the answer is:
freewheel
'coast' is the definition.
(freewheeling is a kind of coasting)
'not bound to turn' is the wordplay.
'not bound' becomes 'free' ('free' is the opposite to 'bound').
'to turn' becomes 'wheel' (I've seen this before).
'free'+'wheel'='FREEWHEEL'
(Other definitions for freewheel that I've seen before include "Go downhill on a bicycle without pedalling" , "The cyclist may" , "powerless to move" , "Coast (on a bicycle) without pedalling" , "Move (by bicycle) without pedalling" .)