Permission to depart (5)
I believe the answer is:
leave
This clue is a double definition.
'permission' is the first definition.
(leave is permission or authorisation)
'depart' is the second definition.
(I know that depart is a more specific form of leave)
'to' is the link.
(Other definitions for leave that I've seen before include "Relinquish - holiday" , "Time off, depart" , "Furlough" , "Permission to do something" , "Exit" .)