Obstacle when getting permit (3)
I believe the answer is:
let
This clue might be a double definition.
'obstacle' is the first definition.
('let' could historically mean an obstruction)
'getting permit' is the second definition.
'let' can be an answer for 'permit' (I've seen this before). I am not certain of the 'getting' bit.
'when' is the link.
Can you help me to learn more?
(Other definitions for let that I've seen before include "Rent out (property)" , "Permitted" , "Allow or rent" , "inefficient service" , "Allow, don't hinder" .)