Journey a mistake (4)
I believe the answer is:
trip
This clue is a double definition.
'journey' is the first definition.
(I've seen this before)
'a mistake' is the second definition.
(trip is a kind of mistake)
(Other definitions for trip that I've seen before include "Journey - miss one's footing" , "Stumble - excursion" , "Short excursion" , "Excursion (while on drugs?)" , "blunder" .)