Gateway structure (4)
I believe the answer is:
arch
'gateway structure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arch that I've seen before include "Teasing; part of foot" , "Curved part of the foot" , "Marble, for example" , "in short, is out of date" , "Mischievous - shrewd" .)