Pass through, carrying last of passengers (4)
I believe the answer is:
visa
'pass' is the definition.
(thesaurus)
'through carrying last of passengers' is the wordplay.
'through' becomes 'via' (I've seen this before).
'carrying' is an insertion indicator.
'last of' says to take the final letters.
The last letter of 'passengers' is 's'.
'via' enclosing 's' is 'VISA'.
(Other definitions for visa that I've seen before include "Mark on passport" , "Travel pass" , "Travel warrant" , "Travel stamp in passport" , "Passport stamp or well-known credit card" .)