Allow, authorise (6)
I believe the answer is:
permit
This clue is a double definition.
'allow' is the first definition.
(I know that allow can be written as permit)
'authorise' is the second definition.
(I know that authorise is a more specific form of permit)
(Other definitions for permit that I've seen before include "Allow - visa" , "Let - pass" , "Let; enabling document" , "Allow; make possible" , "Warrant" .)