Chap goes to base for permit (5)
I believe the answer is:
allow
'permit' is the definition.
('allow' can be a synonym of 'permit')
'chap goes to base' is the wordplay.
'chap' becomes 'al' (**).
'goes to' is a charade indicator (letters next to each other).
'base' becomes 'low' ('low' can be a synonym of 'base').
'al'+'low'='ALLOW'
'for' acts as a link.
(Other definitions for allow that I've seen before include "Permit or concede" , "Licence" , "Give leave to" , "brook" , "praise no more" .)