Vehicle that's hit, but not at first (5)
I believe the answer is:
truck
'vehicle' is the definition.
(truck is a kind of vehicle)
'hit but not at first' is the wordplay.
'hit' becomes 'struck' (strike can mean to hit).
'but not at first' means to remove the first letter.
'struck' with its first letter taken away is 'TRUCK'.
'that's' is the link.
(Other definitions for truck that I've seen before include "Large road vehicle" , "commercial vehicle" , "Lorry - wagon" , "trolley" , "trade" .)