Permission to go (5)
I believe the answer is:
leave
I believe this is a double definition.
'permission' is the first definition.
(leave is permission or authorisation)
'go' is the second definition.
(go can mean to depart or leave)
'to' acts as a link.
(Other definitions for leave that I've seen before include "Relinquish - holiday" , "Permission (to take holidays?)" , "Permission - time off" , "Something taken by those withdrawing" , "Furlough" .)