Letters picked up with a permit (4)
I believe the answer is:
visa
'permit' is the definition.
(I know that visa is a more specific form of the action O.K.)
'letters picked up with a' is the wordplay.
I cannot quite see how this works, but
'up' could be 'is' (I've seen this in other clues) and 'is' is found in the answer.
'a' is found in the answer.
A single letter 'v' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for visa that I've seen before include "travel authority" , "Authorisation to enter a country" , "Travel pass" , "Mark on passport" , "Endorsement allowing bearer to enter country" .)