Stumble on journey (4)
I believe the answer is:
trip
I believe this clue is a double definition.
'stumble' is the first definition.
(synonyms)
'journey' is the second definition.
(trip is a kind of journey)
'on' acts as a link.
(Other definitions for trip that I've seen before include "Ride" , "Hallucinatory experience" , "day out?" , "In close confrontation" , "Accidental misstep" .)