Permit to travel (6)
I believe the answer is:
ticket
'permit to travel' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ticket that I've seen before include "Summons served for some traffic offences" , "Pass or permit" , "Document for traveller" , "Authority for entry, etc" , "Slip to show payment of entrance fee" .)