Sort of vehicle difficult to pass initially (7)
I believe the answer is:
hardtop
'sort of vehicle' is the definition.
'difficult to pass initially' is the wordplay.
'difficult' becomes 'hard' ('hard' can be a synonym of 'difficult'**).
'initially' suggests taking the first letters.
The initial letter of 'pass' is 'p'.
'hard'+'to'+'p'='HARDTOP'
(Other definitions for hardtop that I've seen before include "Rigid-roofed vehicle" , "Car's rigid roof" , "Sort of car" , "Type of car with removable roof" , "Car with rigid roof" .)