Travel permit for small group (7)
I believe the answer is:
triplet
'small group' is the definition.
(I've seen this before)
'travel permit' is the wordplay.
'travel' becomes 'trip' (trip is a kind of travel).
'permit' becomes 'let' (synonyms).
'trip'+'let'='TRIPLET'
'for' is the link.
(Other definitions for triplet that I've seen before include "Group of three equal notes" , "Set of three things" , "One of three born together" , "Baby with two similar siblings" , "one arriving with two others" .)