The most common and most likely answer to this crossword clue is the 7 letter word CONDUIT
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More clues leading to the result CONDUIT
Buddy explains!

The straight part
We know that "passage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case passage = conduit.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CONDUIT mean?
CONDUIT noun- A pipe or channel for conveying water etc.
- A duct or tube into which electrical cables may be pulled; a type of raceway.
- A means by which something is transmitted.
- An investment vehicle that issues short-term commercial paper to finance long-term off-balance sheet bank assets.