Part of passport allowing entrance (6)
I believe the answer is:
portal
'entrance' is the definition.
(portal is a kind of entrance)
'part of passport allowing' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'PORTAL' is hidden in the letters of 'passport allowing'.
(Other definitions for portal that I've seen before include "Grand sort of entrance." , "Gate, entrance" , "Grand and imposing entrance" , "'Doorway, entrance (6)'" , "An imposing gate or doorway" .)