Unfasten lid of vehicle without roof (4-3)
I believe the answer is:
open-top
'vehicle without roof' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'unfasten lid' is the wordplay.
'unfasten' becomes 'open' (I've seen this before).
'lid' becomes 'top' (eg a bottle top).
'open'+'top'='OPEN-TOP'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for open-top that I've seen before include "Lacking cover" , "(Of car) not having a permanent roof" , "Like some tourist buses" .)