Stumble, slip (4)
I believe the answer is:
trip
I believe this clue is a double definition.
'stumble' is the first definition.
(I know that stumble can be written as trip)
'slip' is the second definition.
(I know that slip can be written as trip)
(Other definitions for trip that I've seen before include "blunder" , "(Cause to) fall" , "often occurring just before the fall" , "Journey, excursion" , "a result of drug-taking" .)