The most common and most likely answer to this crossword clue is the 8 letter word SPIRACLE
I've seen this crossword clue in Independent
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The straight part
We know that "passage through rock" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case passage through rock = spiracle.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 SPIRACLE mean?
SPIRACLE noun- A pore or opening used (especially by arthropods and some fish) for respiration.
- The blowhole of a whale, dolphin or other similar species.
- Any small aperture or vent for air or other fluid.