Gambling game permitted during journey (8)
I believe the answer is:
roulette
'gambling game' is the definition.
(roulette is a kind of gambling game)
'permitted during journey' is the wordplay.
'permitted' becomes 'let' (I've seen this before).
'during' indicates putting letters inside.
'journey' becomes 'route' (I've seen this before).
'let' inserted within 'route' is 'ROULETTE'.
(Other definitions for roulette that I've seen before include "Game of chance with small ball" , "risky venture" , "it's for the better, supposedly" , "Wheel for the gambler" , "sort of gambling" .)