Journey allowed, one of three (7)
I believe the answer is:
triplet
'one of three' is the definition.
(one of a set of triplets)
'journey allowed' is the wordplay.
'journey' becomes 'trip' (trip is a kind of journey).
'allowed' becomes 'let' (to let is to allow or permit).
'trip'+'let'='TRIPLET'
(Other definitions for triplet that I've seen before include "One of three children" , "sibling?" , "One of three born at the same time" , "Group of three equal notes" , "One of several arriving together" .)