Allow into journey travelled for gambling game (8)
I believe the answer is:
roulette
'gambling game' is the definition.
(roulette is a kind of gambling game)
'allow into journey travelled' is the wordplay.
'allow' becomes 'let' ('let' can be a synonym of 'allow').
'into' is an insertion indicator.
'journey travelled' becomes 'route'.
'let' put inside 'route' is 'ROULETTE'.
'for' is the link.
(Other definitions for roulette that I've seen before include "Gambling game with spinning wheel and ball" , "it's for the better, supposedly" , "If Russian, it's a very dangerous game" , "Form of gambling" , "risky venture" .)