E-tag, as an opening for passage back (4)
I believe the answer is:
gate
'passage back' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'e-tag as an opening' is the wordplay.
'e-tag' anagrams to 'GATE'.
But, I am unsure how the anagram is indicated.
'for' is the link.
Can you help me to learn more?
(Other definitions for gate that I've seen before include "Doorway" , "Facility in airport" , "Portal" , "It may be barred" , "Field entrance" .)