Tied horse into winter vehicle (8)
I believe the answer is:
shackled
'tied' is the definition.
(thesaurus)
'horse into winter vehicle' is the wordplay.
'horse' becomes 'hack' (hack is a kind of horse).
'into' means one lot of letters goes inside another.
'winter vehicle' becomes 'sled'.
'hack' inserted within 'sled' is 'SHACKLED'.
(Other definitions for shackled that I've seen before include "Restrained" , "In chains" , "Confined, as with fetters" .)