Leave out of the article (4)
I believe the answer is:
Here is my best explanation:
'leave' is the definition.
('exit' can be a synonym of 'leave')
'out of the article' is the wordplay.
'out of' becomes 'ex'.
'the article' becomes 'it' (I can't justify this - if you can you should give a lot more credence to this answer).
(Other definitions for exit that I've seen before include "Relinquish the lead", "Escape route?", "A way out", "Way to go!", "Depart", "Road leaving motorway", "Outlet", "farewell!", "Act of going out" and "Go out".)